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mark6437

Cyanuric Acid Problem

41 posts in this topic

My pool is about 14,000 gallons. It is about 9 years old. I am having a problem with Cyanuric acid. About every 4-5 months my Cyanuric acid level goes above 100 and it locks my chlorine in at either zero or off the charts high. At that point I am told my chlorine no longer does its job. I am also told at that point I have no other choice but to drain/dillute my pool.

I have drained my pool apprx 10-15 times now. I even bought my own sump pump.

There has got to be a reason this keeps happening yet no pool store can tell me why its happening. I have a 3" chlorine feeder that I keep on 2 and a cartridge filter. I clean it regularly and do not have an algae problem or any other problem accept this dang acid level. I even switched to sodium based shock but that did not help. I also tried only putting 2 3" tabs in the feeder at a time. No help.

Does anyone have any idea of how I can fix this? It is really getting annoying. I am ready to fill the pool in with dirt.:(

Thx

Mark

Hou TX

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Mark,

The 3" chlorine feeder uses Trichlor tabs/pucks and these are stabilized chlorine that contains Cyanuric Acid. There are two types of stabilized chlorine, Trichlor pucks/tabs (or sometimes granular) and Dichlor granular/powder. Both will increase Cyanuric Acid rather quickly. Calcium Hypochlorite, aka Cal-Hypo, is another source of chlorine and it does not contain Cyanuric Acid, but does contain Calcium. Chemical facts that your pool store should have told you are the following:

For every 10 ppm Free Chlorine (FC) added by Trichlor, it will also increase Cyanuric Acid (CYA) by 6 ppm.

For every 10 ppm FC added by Dichlor, it will also increase CYA by 9 ppm.

For every 10 ppm FC added by Cal-Hypo, it will also increase Calcium Hardness (CH) by 7 ppm.

Because you have a cartridge filter, you do not backwash weekly, so without significant splash-out you have very little dilution of water in your pool. If your pool was using about 1 ppm FC per day in chlorine, then the CYA would build up by 1*30*0.6 = 18 ppm per month so after 4 months that would increase your CYA by 72 ppm so if you started out with 30 ppm CYA then that would bring you to over 100 ppm CYA. Pretty straightforward and yet your pool store and indeed most of the pool industry doesn't tell you these facts. Instead they just give general statements about how stabilized chlorine can build up CYA over a long period of time, but they don't give you the basic facts that let you calculate exactly how quickly it can occur. The above facts aren't even taught in CPO courses from NSPF or in TECH courses from APSP though my hope is that they will be someday.

To prevent the buildup of CYA, you should be using unstabilized chlorine. Also, to prevent buildup of CH, you should not use Cal-Hypo for too long. This leaves chlorinating liquid, bleach, and lithium hypochlorite as sources of chlorine. Lithium hypochlorite is very expensive, so realistically that leaves chlorinating liquid (typically 12.5% or 10% strength) or 6% unscented bleach (Clorox Regular).

Just using chlorinating liquid or bleach to shock won't help much since the primary problem is the continued use of Trichlor pucks/tabs. You need to stop using those completely. Also, note that you'll want your Total Alkalinity (TA) to be lower, probably not above 80 ppm, if you switch to using chlorinating liquid or bleach or any other hypochlorite source of chlorine including lithium hypochlorite or Cal-Hypo. The reason is that Trichlor is highly acidic so required a higher TA level and also required regular addition of pH Up product. When using the unstabilized chlorines, the tendency will be for the pH to rise and you can minimize that by having a lower TA level (the pH rises mostly due to outgassing of carbon dioxide since pools are intentionally over-carbonated and TA is partly a measure of that).

The downside to using chlorinating liquid or bleach is that you'll need to add it every day or two if you pool is exposed to sunlight and does not have a pool cover. With a pool cover, you could probably add chlorine twice a week. There are ways to automate the chlorine dosing including The Liquidator but this is not issue-free. There are also peristaltic pumps. Finally, one can get a saltwater chlorine generator (SWG) system, but you need to be careful about the type of stone around your pool and exposure to some types of metal due to the higher salt content of the water. Another downside to the chlorinating liquid or bleach is that these are less concentrated forms of chlorine by weight so it's heavier to carry (it's mostly water).

What you have been going through is similar to what I went through when I first got my pool 6 years ago. I used Trichlor pucks/tabs in a floating feeder and I has an opaque pool cover so my chlorine usage was low at around 0.6 ppm FC per day. I also had a cartridge filter and minimal splash-out. So after one and a half seasons (about 11 months of non-winter use), my CYA got to around 150 ppm and the water turned dull and I couldn't keep up with chlorine demand. I had the beginnings of algae growth (though didn't know it at the time) even though I used an alagecide but only every other week. The floating feeder also parked itself near some stainless steel bars and the mounts rusted due to Trichlor's high acidity. The pool store was of no help. That's when I decided to learn pool water chemistry for myself. I now use only 12.5% chlorinating liquid from my local pool store and add it twice a week to my pool. I only need to add a small amount of acid every 3-4 weeks because the pH is very stable. The pool is in use more now so uses almost 1 ppm FC per day on average. The water is crystal clear and I only spend around $15 per month on chlorine and acid for a 16,000 gallon pool.

You can learn much more about how to maintain your pool by reading the Pool School at Trouble Free Pool.

Richard

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Mark,

For every 10 ppm Free Chlorine (FC) added by Trichlor, it will also increase Cyanuric Acid (CYA) by 6 ppm.

For every 10 ppm FC added by Dichlor, it will also increase CYA by 9 ppm.

For every 10 ppm FC added by Cal-Hypo, it will also increase Calcium Hardness (CH) by 7 ppm.

To prevent the buildup of CYA, you should be using unstabilized chlorine. Also, to prevent buildup of CH, you should not use Cal-Hypo for too long. This leaves chlorinating liquid, bleach, and lithium hypochlorite as sources of chlorine. Lithium hypochlorite is very expensive, so realistically that leaves chlorinating liquid (typically 12.5% or 10% strength) or 6% unscented bleach (Clorox Regular).

Richard

Richard, I agree with everything you said, but you have forgot to mention the 2 drawbacks of liquid chlorine. 1) liquid chlorine will raise your TDS more then any other chlorine, and 2) why is stabilized chlorine better then unstabilized chlorine?? because the sun dissipates unstabilized chlorine out of the water rapidly. So if the pool is in the sun, you will need to add chlorine daily, or even twice a day. the exception will be pools that are not in the sunlight much due to indoor or automatic covers.

More info on CYA levels ......... CYA level can go as high as 150 without ill effects most of the time ......... CYA level will stay below 100 normally due to dillution by rain, and having to refill pool with fresh water due to splash out, backwash, evaporation, ect. The biggest culprit to high CYA levels is automatic covers that do not allow the above mentioned.

OK I think this topic is well covered now.. lol

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Richard, I agree with everything you said, but you have forgot to mention the 2 drawbacks of liquid chlorine. 1) liquid chlorine will raise your TDS more then any other chlorine, and 2) why is stabilized chlorine better then unstabilized chlorine?? because the sun dissipates unstabilized chlorine out of the water rapidly. So if the pool is in the sun, you will need to add chlorine daily, or even twice a day. the exception will be pools that are not in the sunlight much due to indoor or automatic covers.

More info on CYA levels ......... CYA level can go as high as 150 without ill effects most of the time ......... CYA level will stay below 100 normally due to dillution by rain, and having to refill pool with fresh water due to splash out, backwash, evaporation, ect. The biggest culprit to high CYA levels is automatic covers that do not allow the above mentioned.

OK I think this topic is well covered now.. lol

For every 10 ppm FC from ANY source of chlorine, the chlorine will convert to chloride (salt) as it gets used up and will increase salt by 6 ppm [EDIT] actually, it's 8.2 ppm [END-EDIT]. With most hypochlorite sources of chlorine (except Cal-Hypo), the initial addition of chlorine increases salt by 6 ppm [EDIT] actually, 8.2 ppm [END-EDIT] so the net increase including accounting for consumption is 12 ppm [EDIT] actually, 16.4 ppm [END-EDIT]. The thing is that this doesn't matter very much as it takes a long time for the salt level to get high. Remember that SWG pools have 3000 ppm salt level.

As for CYA up to 150 ppm having no problems, that very much depends on the pool's nutrient levels. If there are phosphates in the pool, then you can get green algae growth whenever the FC level drops below about 5% of the CYA level. As for keeping CYA lower, that only happens if you have significant water dilution as would occur in a smaller pool with a shorter swim season using a filter such as sand that was backwashed weekly. In my own pool that I first installed 6 years ago, I initially used Trichlor pucks/tabs and even with low chlorine use of only about 0.7 ppm FC per day, I got to 150 ppm in one and a half seasons. I have a cartridge filter and a 16,000 gallon pool and 7-month long swim seasons. 0.7*7*1.5*30*0.6 = 132 ppm above my initial 30 ppm with some small amount of splash-out. I started to have my water turn dull and have unusual chlorine demand (nascent algae growth) even though I was using PolyQuat 60 algaecide, but I was using it every other week. Had I used the algaecide every week, I probably could have gone longer. I also rusted some stainless steel mounts when the Trichlor feeder parked itself nearby.

I have an automatic cover, but that has nothing to do with dilution since evaporation does not dilute CYA. When water evaporates, it leaves the pool while the CYA stays in the water getting more concentrated (imagine what would happen if half of the water evaporated -- the CYA concentration would double since there's the same amount of CYA in half the amount of water). When the fill water fills it back up, it dilutes right back to where it started. The amount of CYA (or any other chemical that isn't volatile) doesn't change from evaporation -- only from physical removal of water AND CYA as occurs with splash-out or backwashing. Evaporation will increase the levels in the pool of whatever is in the fill water, such as Calcium Hardness (CH).

By the way, I'm not saying that you shouldn't have CYA in the pool. As you point out, you need it to prevent chlorine from breaking down too quickly by the UV rays in sunlight and also need it to moderate chlorine's strength (chlorine without CYA is too strong at normal FC levels). I'm just saying that you need to be careful if you use stabilized chlorine products as the CYA can build up quickly depending on the situation.

Richard

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good points Richard. TDS is total disolved solids, having little to do with salt levels. I guess I am glad our pool has a diving board so I get plenty of splash out, along with a earth filter, so I do loose water when I backwash. thus my cya level is below 100. I forgot to mention draining the pool down for winter and being dilluted all winter with the mesh cover on it. So high cya levels are not a problem around here as most pools are like mine.

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good points Richard. TDS is total disolved solids, having little to do with salt levels. I guess I am glad our pool has a diving board so I get plenty of splash out, along with a earth filter, so I do loose water when I backwash. thus my cya level is below 100. I forgot to mention draining the pool down for winter and being dilluted all winter with the mesh cover on it. So high cya levels are not a problem around here as most pools are like mine.

The part about TDS is absolutely not true. TDS, or Total Dissolved Solids, absolutely positively includes salt. Sodium Chloride salt, as well as calcium chloride and sodium bicarbonate are all Dissolved Solids. Salt dissolves in water, after all. They are all ions in the water and they all contribute to the conductivity measured by a TDS meter. The TDS in a pool with 3000 ppm salt is roughly 3200 ppm with the difference due to the bicarbonate and calcium and even CYA itself (mostly as cyanurate ion) that is additional to the salt (you can't just add the ppm values together, however, since they are in different units with TA and CH measured as ppm Calcium Carbonate equivalent). TDS by itself is a pretty useless measurement. It's what is composed in TDS that is relevant. Historically, many people thought that high TDS caused problems with algae growth, but it was really the higher CYA (without correspondingly higher FC) that was the cause -- it just turned out that higher CYA and higher TDS were correlated since the higher TDS (from chloride, CYA and added base that compensates for pH) and the CYA both came from the same source over time, Trichlor.

Yes, if you drain the pool down for winter, that certainly dilutes as well. So does winter rains assuming the water overflows. In fact, I am diluting my pool water with winter rains this year since the salt level has creeped up to around 1500 ppm after 3-4 years without such dilution. There's no problem, but I thought I'd take care of that this year.

Just keep in mind that chlorine usage of even 1 ppm FC per day using Trichlor adds over 100 ppm to CYA in just 6 months if you aren't diluting through weekly backwashing or significant splash-out. There are many, many people who have had problems with algae in their pools who report on multiple pool forums including The Pool Forum and Trouble Free Pool. Many of these pools have algae problems with CYA below 100 ppm. If you only keep an FC of 3 ppm, then you can get green algae in the pool with a CYA of 80 ppm. Even saltwater chlorine generator (SWG) pools with 1-2 ppm FC and 80 ppm CYA have had green algae growth, oftentimes looking like mysterious chlorine demand at first. The rule of a minimum FC that is 5% of the CYA level for SWG pools means that at 80 ppm CYA you need a minimum of 4 ppm FC and even 3 ppm FC is not enough for a few pools (usually those with higher phosphate levels).

Richard

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Richard, again you are correct. I thought about wording my statement differently, and I guess I should have now. TDS has does not really say you have salt in the water, but TDS will go up as the salt levels do. TDS is measuring all dissolved solids in the water. The reason you have a higher tds when using liquid chlorine is because liquid chlorine is sodium hypochloride, which contains salt. So all I am saying is that TDS levels will be the highest in pools that use liquid chlorine, with the sodium causing that. used to be that when tds got 1000-1500, pool stores would tell you to do a partial drain to dillute it, as you might have a hard time dissolving any solids in it. Well now with salt water systems, tds is up to 4600 or more, with salt levels being at 3200.

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Richard, again you are correct. I thought about wording my statement differently, and I guess I should have now. TDS has does not really say you have salt in the water, but TDS will go up as the salt levels do. TDS is measuring all dissolved solids in the water. The reason you have a higher tds when using liquid chlorine is because liquid chlorine is sodium hypochloride, which contains salt. So all I am saying is that TDS levels will be the highest in pools that use liquid chlorine, with the sodium causing that. used to be that when tds got 1000-1500, pool stores would tell you to do a partial drain to dillute it, as you might have a hard time dissolving any solids in it. Well now with salt water systems, tds is up to 4600 or more, with salt levels being at 3200.

Water Saturation

Yeah, pool stores have said lots of things that aren't true. It is not true that a higher TDS makes it harder to dissolve any solids in it. Water simply doesn't get saturated that way. Saturation occurs for each chemical compound separately where the product of concentrations of the component species exceeds the solubility product at which point one gets precipitate. This is done intentionally for calcium ions and carbonate ions, for example, through adjustment of TA (adjusted for CYA), CH and pH though there is also a dependency on temperature and TDS. Even for calcium carbonate, however, it is able to dissolve more readily at higher TDS levels. This is because TDS, especially when measured using a conductivity meter (as opposed to evaporation of water with measurement of resulting solids) is related to the ionic strength of the water and higher ionic strength makes charged species (ions) behave as if they are at lower concentrations then they actually are -- essentially, the higher ionic strength means that ions "shield" other ions in terms of their electrostatic potential and that makes them less reactive behaving as if they are less concentrated. Basically, this means that salt pools require a higher TA, CH and/or pH combination (at the same CYA level) as non-salt pools in order to prevent plaster corrosion.

The saturation limit for salt (sodium chloride) in water is roughly 360,000 ppm (35.9 g/L) so well beyond what even sea water contains (sea water is roughly 35,000 ppm). Cyanuric Acid (CYA) has a solubility limit of around 2000 ppm. Sodium Bicarbonate (baking soda; Alkalinity Up) has a solubility limit of around 78,000 ppm. In practical terms, it is Calcium Carbonate that is the primary saturation factor one should be concerned about. If the water is not saturated with calcium carbonate, then plaster/grout can dissolve; if the water if over-saturated with calcium carbonate, then scale can form. The saturation index may be calculated from the other water parameters by using The Pool Calculator. Other substances where solubility is particularly important are other metal ions including copper and silver since these can precipitate as metal stains if these concentrations get too high and/or the pH gets high. The limited solubility of Lanthanum Phosphate is intentionally used in phosphate remover products since they contain Lanthanum Chloride and forcibly precipitate phosphate out of the water.

Chemical Additions

Though it is true that sodium hypochlorite contains salt and therefore has the salt and TDS levels rise faster when you use that source of chlorine, it is also true that ALL sources of chlorine result in a salt and TDS rise (unless there is dilution) because when chlorine gets used up it gets converted to chloride. This occurs when it breaks down from sunlight or when it oxidizes ammonia or organics. As I mentioned before, sodium hypochlorite adds salt twice as fast as Trichlor and Dichlor, but they all increase salt levels and that isn't a big deal. The CYA added from Trichlor and Dichlor are a MUCH bigger deal since they add proportionately much more CYA relative to normal CYA levels than they add to salt. Cal-Hypo increases Calcium Hardness (CH), but it too adds proportionately less relative to normal levels. As a specific example, let's assume a pool has a CH of 300 ppm, CYA of 50 ppm, salt level (roughly TDS) of 750 ppm. Adding 1 ppm FC per day for 1 month does the following:

[EDIT] I corrected the salt levels below for all sources [END-EDIT]

With Trichlor, CYA increases by 18 ppm so by 100%*18/50 = 36%

With Trichlor, salt increases by 25 ppm so by 100%*25/750 = 3.3%

With Dichlor, CYA increases by 27 ppm so by 100%*27/50 = 54%

With Dichlor, salt increases by 25 ppm so by 100%*25/750 = 3.3%

With Cal-Hypo, CH increases by 21 ppm so by 100%*21/300 = 7%

With Cal-Hypo, salt increases by about 31 ppm so by 100%*31/750 = 4.1%

With Sodium Hypochlorite (or lithium hypochlorite), salt increases by 49 ppm so by 100%*49/750 = 6.5%

You can see that Trichlor and Dichlor proportionately increase CYA by a lot. As noted earlier, one can run into problems in just one season, depending on the specific situation (i.e. rate of dilution). To keep the CYA constant from use of Trichlor would require dilution of the water every month by 26%. To prevent algae growth, one has several alternatives when the CYA is higher: 1) raise the FC proportionately to keep the FC/CYA ratio constant (see this chart or 2) use an alagecide (e.g. PolyQuat 60 weekly) or a phosphate remover.

Cal-Hypo increases CH, but not that much proportionately so it takes a while before it affects the saturation index in a serious way. Even after 6 months, the CH would only rise from 300 ppm to 426 ppm raising the saturation index by 0.12 units which isn't very much -- over several years or with higher chlorine usage this could be a problem, but to go from 426 back to 300 ppm using fill water with no CH requires a dilution of 30%.

Sodium Hypochlorite increases salt faster, but proportionately it's far less than the rate of CYA increase from Trichlor and Dichlor and is even less than the rate of increase in CH from Cal-Hypo. Even after 6 months, the salt would only rise from 750 ppm to 1044 ppm and would require 28% dilution to get the salt level back down.

TDS and "age" of water

The one possible reasonable use for TDS (other than in the calcium carbonate saturation index calculation) is as a proxy for the "age" of the water. When a pool gets used over time by bathers, they do introduce a variety of organic substances into the water some of which do not get readily oxidized or broken down so may become insoluble more readily. An extreme example of this is with lotions and oils that form on the water or produce gummy scum lines (not scale, which is calcium carbonate). However, since this effect is dependent more on bather load than on the age of the water (represented by the cumulative amount of chlorine that is added over time), TDS isn't a very good parameter to use for this purpose. Perhaps some combination of TDS, type of chlorine used, and typical bather load would be useful. A formula used in spas for determining when a water change is needed is the following:

Water Replacement Interval (WRI) = (1/3) x (Spa Volume in U.S. Gallons) / (Number of Bathers per Day)

The main problem with the above forumla is that it does not account for different soak times since soaking longer results in more bather waste products. The above probably assumes an average soak time of around 15-20 minutes. A better formula would use a bather-hour parameter. For pools, a proposed rule from APSP is to replace 7 gallons of pool water per bather (and again, this really should be based on bather-hours).

The main fallacy of using TDS, however, is that it doesn't take into account bather load. If you weren't using an outdoor pool at all, you'd still need to add chlorine regularly due to breakdown of chlorine from sunlight (even with CYA protecting it), so TDS will rise but there would be no bather wastes. The pool water does not go "bad" in this situation. The salt level rises, but as noted above, that's not a problem until the salt gets very high. At high bather loads, most of the chlorine is used to oxidize the ammonia and urea from sweat and urine so here TDS is a reasonable proxy for that bather load, BUT one must take into account the type of chlorine being used. Sodium Hypochlorite will increase TDS (and salt) twice as fast as Trichlor for the same amount of chlorine so equating TDS to the amount of bather waste in conditions of high bather load means you have to account for that and allow for a greater rise in TDS when using sodium hypochlorite. That is, a rise in TDS of 500 with Trichlor is the same as a rise in TDS of 1000 with Sodium Hypochlorite in terms of what it means for the amount of chlorine that has cumulatively added and the presumed amount of bather waste in a high bather load scenario.

pH of Chlorine Products

Another fallacy told by most pool stores and the industry as a whole is that Dichlor is close to pH neutral while the hypochlorite sources of chlorine, including Sodium Hypochlorite, are high in pH. This is only true for the initial chemical addition, but neglects to take into account what happens when the chlorine gets used up (consumed). The consumption of chlorine is an acidic process and makes the ongoing use of Dichlor net acidic and the ongoing use of hypochlorite sources of chlorine close to pH neutral (except for the small amount of "excess lye" in these products). I only use 12.5% chlorinating liquid in my pool at a rate (during the summer) of around 1 ppm FC per day. Based on the pH of the added chlorine, I should see my pH rise from 7.5 to 7.8 in just one week and to 8.6 in one month, but in fact my pool's pH is very stable rising around 0.1-0.2 over about 1 month. The reason is that the consumption of chlorine is acidic as detailed in this post.

pH Rise from TA in Pools

So where does the rise in pH in many pools come from? It comes from the fact that pools are intentionally over-carbonated which is what Total Alkalinity (TA) mostly measures (it mostly measures bicarbonate). This over-carbonation is intentional in order to provide a pH buffer to minimize swings in pH and in order to saturate the water with calcium carbonate in order to prevent dissolving of plaster. However, this over-carbonation leads to the outgassing of carbon dioxide from the pool into the air and this makes the pool rise in pH (you are essentially removing carbonic acid from the water; removing an acid makes the pH rise). This outgassing occurs faster at higher TA levels, lower pH and with more aeration of the water. It turns out that the effect of higher TA on the outgassing rate is greater than the effect of TA on pH buffering so the net result with higher TA is a faster rise in pH over time. So the solution is simply to maintain a lower TA level (adjusting CH and pH as appropriate to maintain a saturation index near zero). These same principles apply to saltwater chlorine generator (SWG) pools as well, though there are some other factors that may be at play there such as chlorine outgassing (from undissolved chlorine gas).

Richard

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Richard, I just joined the forum after stumbling across it while looking for info on liquid chlorine for addition to my 27,000 pool in central Texas. Your knowledge of pool chemistry and willingness to share it is AWESOME !! As hot as it gets in Texas, my 20 year old pool has finally stabilized with absolutely no trouble for the past few years, with a sanitizing combination of MPS, CalHypoChlorite, and a few tabs in a floater, but I think the key is regular adds of a product called NoMorProblems. I also have had concerns with high CYA levels, which is my reason for investigating cutting off the stabilized tabs and going to liquid chlorine. Any comments on the NoMorProblems additive?

Dan

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Dan,

If you want to learn more about how to maintain a pool, read up at the Pool School at Trouble Free Pool. You can prevent algae growth simply by maintaining a Free Chlorine (FC) level appropriate to the Cyanuric Acid (CYA) level. For manually dosed pools, that's a minimum FC of around 7.5% of the CYA level. You wouldn't need any additional additives (at extra cost) if you were to do that.

If you don't want to maintain the appropriate FC/CYA ratio, then you have to use either a supplemental algaecide weekly such as PolyQuat 60, or use a phosphate remover unless you happen to be lucky and have a pool very low in phosphates already. I have never been able to find out what the ingredients are in NoMorProblems so can't really comment on it specifically (I speculate below).

Are there any ingredients listed on the label? The MSDS at the United Chemical site just says its contents are proprietary. Their description here says that it is not a polymer yet acts as a clarifier. They say that by using their product you no longer need to shock, but I can tell you that simply maintaining an appropriate FC/CYA ratio you also never need to shock -- I didn't have to shock the pool at all this past swim season. They say that it increases chlorine demand in the short-run so I'm guessing that the product is an enzyme that catalyzes (accelerates) oxidation which would breakdown substances that could otherwise make water cloudy. It may also facilitate the killing of algae by chlorine. That would be my best guess. There are other enzyme-based products on the market and they have similar effects, though I can't comment on whether they are better or worse (e.g. Natural Chemistry Pool Perfect).

NoMorProblems is not necessary if you maintain the proper FC/CYA ratio, but it won't hurt so if you don't mind spending extra money or don't want to maintain appropriate chlorine levels, then it's something extra to use. In my own 16,000 gallon pool, I only use 12.5% chlorinating liquid from my pool store that costs me around $15 per month and that's all I use except for a small amount (2 cups) of acid about once a month.

Richard

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Richard, the Pool School is a GREAT resource.

Incidentally, the bottle of MoMorProblems has no more info than the MSDS.

Thanks much for the advice.

Dan

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NoMorProblems is sodium bromide. Their labeling (and most of the industry) is made for pools up north. In Texas, I saw many pools that needed over 5 tabs added every week this last summer as water temperatures approached 95 degrees. Much of this was info from customers but I did see it myself in a few pools I maintained. The hot water does not hold chlorine at all.

But it holds bromine.

I dont fully understand bromine, as it needs chlorine or Monopersulfate to act as a catalyst. So if most of the chlorine burns out of the water how does the water suddenly stay algae free just by adding sodium bromide (which needs chlorine to act??) Strange stuff. But in Texas, I would put any pool on it.

As I said the instructions are cryptic and talk about how much chlorine you add to the pool. But they dont take into account water temperature at all, so the dosage you actually need are far less then recommended. Otherwise, when you test you will see no FC at all.

I must also say that chemgeek's calculations could be problematic for this region for the same purpose. Do you know the ppm of CYA added by each dichlor and trichlor per pound by any chance? Your calculations certainly show why people should drain often if they choose to use trichlor tabs. What I mean is, maintaining 1ppm FC at 90 water temperature would build up stabalizer EVEN QUICKER then at 75 or whatever your regional water temp sits at (as more tabs would be required to maintain it.) This will be the only time I mention this, as you obviously know more about chemistry than me and your calculations do a huge service to helping people understand the problem with CYA.

There is much that is not taught in the CPO course. The handbook they give you is quite informative though on a number of subjects.

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So if it's sodium bromide, then that turns the pool into a bromine pool. Any chlorine in the pool will get consumed and convert bromide to bromine. Bromine will break down faster in sunlight than chlorine, but you also cannot measure bromine separately from chlorine nor can you measure the bromide level (separate from chloride). So if you are seeing that bromine holds better, then it's probably not due to any difference in the rate of breakdown from sunlight, but probably from chlorine previously getting used up faster battling algae. Because bromine doesn't combine with CYA, it's already at 10-30 times the effective concentration of chlorine with CYA and at that concentration is better fighting algae.

It's not that the hotter pool water does not hold chlorine, but rather that the Free Chlorine (FC) levels are too low relative to the Cyanuric Acid (CYA) levels so algae is able to grow about as fast as chlorine can kill it, resulting in an increased chlorine demand and inability to maintain chlorine level. Adding more tabs just makes things worse as that increases the rate of increase in the CYA level, not just FC. In order to keep the pool algae free, one should maintain a minimum FC in a manually dosed pool of at least 7.5% of the CYA level. So at 30 ppm CYA that's only 2.2 ppm FC, but at 80 ppm CYA the minimum FC is 5.8 ppm (see this chart or this chart.

Are you sure that NoMorProblems is sodium bromide? It's true that United Chemical (originally with Jock Hamilton) were big promotors of sodium bromide, but the description of NoMorProblems describes a greater chlorine demand initially that then levels off. They also describe great water clarity after a few weeks. Both of these results would be seen with enzymes, but sodium bromide wouldn't improve water clarity except from clearing dull or cloudy water that was from a nascent algae bloom. It would take enzymes or a clarifier or ozonator to make the water much clearer, though with a decent filter (e.g. DE) and chlorine alone the water clarity can be excellent.

The reason I quote the amount of CYA added relative the amount of FC that is added is that this is independent of concentration of product and of volume of the pool. Nevertheless, if you want amounts for one pound of product in 10,000 gallons, this is as follows, though obviously needs to be scaled appropriately for different pool volumes (larger volume dilutes more so would result in proportionately lower FC or CYA; likewise, for the FC or CYA indicated, a larger pool volume would require proportionately more weight of product).

One pound of Trichlor in 10,000 gallons increases Free Chlorine (FC) by 11.0 ppm and Cyanuric Acid (CYA) by 6.7 ppm.

One pound of Dichlor (dihydrate) in 10,000 gallons increases FC by 6.6 ppm and CYA by 6.0 ppm.

One pound of Cal-Hypo (65%) in 10,000 gallons increases FC by 7.7 ppm and Calcium Hardness (CH) by 5.5 ppm.

One pound of Trichlor is two 3" tablets if these are 8 ounces weight each.

Obviously, the least expensive way to maintain a pool is simply to maintain a sufficient FC level relative to CYA and this implies using unstabilized chlorine once you are at a CYA level that sufficiently protects chlorine from sunlight. The problem is that unstabilized chlorine is not conveniently dosed unless you have a perstaltic pump or The Liquidator (but that can have issues as described here and here). Chlorinating liquid or bleach are much heavier to carry (i.e. less dense forms of chlorine) than Trichlor. Trichlor's main advantage is that it dissolves slowly so can be used in a floating feeder or inline chlorinator, but it's main downsides are its acidity requiring pH compensation and that it increases CYA over time. If one has a pool cover opaque to UV, then one can usually add chlorine twice a week; otherwise, one needs to add chlorine every day or possibly two, depending on CYA level and amount of sunlight.

If you want to use stabilized chlorine and don't want to worry about the CYA level, at least for a while, then you can control algae through other means. Though converting to a bromine pool is one (expensive) method, you can also use a weekly PolyQuat 60 algaecide or you can use a phosphate remover (both at around $2-3 per week). You could use a copper-based algaecide, but that can stain plaster if the pH rises or too much is dosed and it can have blond hair get a greenish tint. So there are several alternatives.

Not everyone sees the CYA level climb quickly. Sometimes it rises more slowly due to greater dilution, such as from smaller pools with more frequent backwashing and winter or summer rains and overflow. In some hot environments, chlorine itself may slowly break down CYA but not all pools see this so it may be catalyzed (sped up) by some other factors (maybe the presence of metal ions, such as iron).

Richard

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Gracias on the info.

Yeah every bottle of NoMorProblems ive seen says "sodium bromide 40%" on the front. (The only other product ive seen with this is "jacks magic yellow stuff 98% sodium bromide.") Its been mysterious for me and I dont like using things i dont fully understand but I use it because it works for me. Some of the pools I take care of do have a high CYA and refuse to drain despite my warnings of plaster degradation and disease, so the bromine is obviously helping with this (as bromine cannot be stabalized.)

I put 1-3 ounces in every pool without fail once it becomes warm.

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Ok I have been gone for a while. I appreciate all of the replies. I am a little confused though.

I need to switch to liquid chlorine?

Oh, as I type this I am draining my pool again.

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To avoid draining your pool, you need to use unstabilized chlorine so if you don't want to build up either Cyanuric Acid (CYA) nor Calcium Hardness (CH) then this means using chlorinating liquid or bleach (Clorox regular unscented or off-brand Ultra) or lithium hypochlorite (but the latter is very expensive). You can get automated dosing systems, such as The Liquidator or a peristaltic pump or you can convert to a saltwater chlorine generator (SWG) system.

If you get a pool cover, you should find that your chlorine usage drops a lot. The main downside to the liquid chlorine approach is that you need to add it every day or two unless you have a pool cover in which case you can usually add it about twice a week. Don't forget that even when using unstabilized chlorine, you do want to initially add some CYA to the water to protect the chlorine from breakdown from sunlight and to moderate its strength.

If you properly maintain your pool's chemistry levels, you will likely never or very rarely need to shock. You would NEVER use Dichlor to shock the pool -- just shock with chlorinating liquid or bleach (if needed).

Another alternative is to do regular water dilution (more continuous or frequent) instead of full drain/refill. Yet another alternative is to ignore the higher CYA and use an algaecide (PolyQuat 60) weekly or a phosphate remover to prevent algae growth, but the sanitation level of the pool will continue to drop as the CYA gets higher unless you proportionately increase the FC level (which is impractical if you use only Trichlor tabs).

Note that even using chlorinating liquid or bleach, you will still need to dilute your water -- just not as much. If you have winter or summer rains and can have them overflow the water or if you can do a partial drain after a rain then that would help greatly. Even in the worst case, you wouldn't need to do more than a 50% partial drain/refill each year, but could probably get away with 20-30% to keep the salt level in check. In my own pool that also has a cartridge filter like yours, I use winter rains to dilute the water, but I have a pool cover so probably use half the daily FC amount you will use.

I again refer you to the Pool School for more details.

Richard

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Richard, your grasp of pool water chemistry is impressive. I do however, have one question for you. How often are you checking and/or adding chemicals to your pool? Are you doing this once a week? Every other day, or twice daily, etc???

Thanks,

Paul

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I appreciate all the experience and information here, and it's very helpful to a new pool owner like myself, I do still have a few questions that I hope you all can help me with.

I just took over care of my new 14,000 gallon gunite/concrete/plaster pool, with an integrated hot tub with 3 spills, DE filter.

I live in FL, the pool is screened in, and the water temp is generally around 86 degrees.

I brought a sample of my water to my local Leslies pool store, they told me a few things. First, my CYA level was high, so, no more tabs, and from what I've been reading, tabs aren't a good way to go anyway since they build up your CYA levels with continued use. So, fine, no tabs. They also said my phosphates were high, they had me do 32 oz of Phosfree, running the pump continuously for 48 hours, it clearly reduced my flow rate as my spills started barely trickling, backwashed my DE filter when the 48 hours were up, flow back to normal, they say my phosphates are better, but still a little high, they said to use a capful once a week.

Now, here's where I think they are leading me astray, based on what Richard and others are saying.

They are essentially having me maintain my FC level by adding a 1 lb. bag of cal hypo shock powder once every 5 days or so. From what I gather, eventually, this will cause an undesired calcium buildup in my pool, so this doesn't seem to be a good long term method of chlorination.

My gut feeling is to use liquid chlorine, but, my pool does get a lot of direct sunlight from the strong FL sun, and without stabilizer, I wonder how effective or long lasting it will be, I really don't want to have to add chlorine every day, but I would if that were the best way to go.

To that end, let's say for a moment, I decide to stop the cal hypo shock powder the store recommends, and just keep a good supply of 12% liquid chlorine on hand, about how often do I add it, and, how much at a time? And, when needed, how do I add some stabilizer, just use pucks for a week or 2? And, if I'm maintaing the FC level with LC, do I still shock the pool periodically, and if so, with LC or powder?

Should I add muratic acid every time I add chlorine, since I was told the chlorine raises ph, or weekly, or only when the ph gets critically high? How much acid do I add to lower a high ph?

I did get the accucheck test strips, but find them not very accurate or reliable, so, I'm going to get a decent test kit tommorrow.

Basically, for my pool, given the above conditions, should I use liquid chlorine, if so, how much and how often, do I add acid weekly, or only if the ph gets too high? If I do switch to liquid chlorine, I assume I should monitor my CYA levels, and add some if it gets low? What about shocking, not neccessary if I keep my FC levels good?

I have to admit, this all seems a little complicated, and I'd very muich appreciate some clarity. (no pun intended. :) )

Thanks so much, Ari

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Richard, your grasp of pool water chemistry is impressive. I do however, have one question for you. How often are you checking and/or adding chemicals to your pool? Are you doing this once a week? Every other day, or twice daily, etc???

Thanks,

Paul

Paul,

Because I have an opaque automatic pool cover, my chlorine usage is relatively low at around 1 ppm FC per day in a 16,000 gallon pool and that's with daily 1-2 hour use. So I only add chlorine twice a week and check it's level at that time (both FC and CC using a FAS-DPD chlorine test). Since my pH and other parameters are very stable, I usually only check the pH every few weeks though in most pools you want to check at least the pH more often -- it's just that in my pool I've got it so it's very stable and I only have to add a small amount of acid every 1-2 months. I only test TA, CH and CYA about twice a swim season, usually upon opening and then again around mid-to-late season. Again, this is because I now "know" my pool pretty well.

To me, this is pretty easy, but even I screw up once in a while. You can read about such a mistake I made here. Because of the high phosphate level (2000-3000 ppb) in my pool, it's very unforgiving if you let the chlorine get to zero, though this was the first time that my CYA got converted to ammonia and intermediate products by bacteria -- and so quickly besides. Definitely a learning experience.

Richard

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Ari,

First of all, you should definitely get a good test kit and I would recommend either the Taylor K-2006 you can get at a good online price here or the TF100 test kit from tftestkits.net here with the latter kit having 36% more volume of reagents so less expensive "per test".

If your pool is exposed to direct sunlight, even if partially filtered by a screen, you will want to have the CYA level up a bit. You always want at least some CYA in the water to moderate chlorine's power, but in your case you might want as much as 60-80 ppm CYA -- I'd start with 50 ppm and see how things go with chlorine consumption/usage. However, you will need to maintain a higher Free Chlorine (FC) level to prevent algae growth unless you want to go the route of always adding a maintenance dose of a phosphate remover (at extra cost). You could go either way -- up to you. Read up at the Pool School, especially the chlorine/CYA chart, if you don't plan to use an algaecide or phosphate remover.

You are correct that the Cal-Hypo will build up your Calcium Hardness (CH). So using chlorinating liquid (or bleach) is your best bet, at least as your primary source of chlorine. You can always use Cal-Hypo when you want to raise your CH and you can always use Trichlor or Dichlor if you want to raise your CYA. If you need to raise your CYA more quickly, then you can either dissolve CYA in a skimmer sock in your skimmer or have it get caught in the filter and don't backwash (though this takes longer to dissolve). If you use Dichlor, then this dissolves quickly, but it also adds chlorine so you can only dose this at the rate you use chlorine. For every 10 ppm FC added by Dichlor, it also increases CYA by 9 ppm. If you are going to add a lot of CYA and need to do so soon, then adding pure CYA via the skimmer is the best way to go. If you use a skimmer sock or old T-shirt, then that has it dissolve pretty quickly -- just make sure you have other sources of flow to your pump such as main drains or a bypass in the skimmer since the CYA in the skimmer sock or T-shirt will clog the flow until it dissolves. Another alternative is to put the CYA in a sock or panty hose and hang it over a return flow.

Note that you do get some dilution from cleaning your DE filter, though perhaps not as much as those that backwash weekly with a sand filter, though definitely more than those who have a cartridge filter. You also may get dilution from rains, if they overflow the pool water (if they just raise the level a bit that then evaporates, then nothing changes chemically).

I'm not so sure how they say you can only add chlorine once every 5 days unless your pool doesn't really get much sun. With an uncovered pool in direct sunlight and without a pool cover, you usually have to add some chlorine every day or two unless you don't mind large FC swings.

As for the pH, you can have it be very stable if you lower the TA level. Chlorinating liquid, bleach, Cal-Hypo and lithium hypochlorite are all close to pH neutral when accounting for chlorine usage/consumption because such usage/consumption is an acidic process the compensates for the initial pH rise upon addition (a technical explanation of this is here). My pool's pH is very stable and I add 1 ppm FC per day of 12.5% chlorinating liquid (added about twice a week because I have an opaque electric pool safety cover). Just note that if you use bleach instead of chlorinating liquid, that Clorox regular unscented has the lowest "excess lye" whereas most off-brand Ultra bleaches have more so have a higher pH which will cause a slow pH rise over time. Chlorinating liquid also has some excess lye, roughly between Clorox and Ultra bleaches (relative to FC amount).

Shocking the pool is not necessary if you keep your levels well maintained. Last year, I don't think I had to shock the pool even once.

Richard

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Richard I am still a little confused. If I switch to Liquid Chlorine cant I just add stabilizer and not have to add LC every day or everyother day? Adding LC everyday is a bit of a turn off but so is draining my pool every 4 months (Ijust got done filling it backup).

I think I may know why I have this problem so often. I do not have one of those auto drains. What I mean is I do not have an overflow protection. So my pool does not automatically expel water when it gets too high. I have to open a valve and the excess gets pumped from the skimmer out a water hose coming from the pump area that I buried going out my back fence. So, the top level of excess water (whcih contains the highest concentration of CYA I think) does not get expelled very often.

I may take your recommendation and pump 2 or 3 inches off the top once a month, unless I switch to LC.

Thx for your help!

Mark

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Mark,

You can have a higher level of stabilizer, around 70-80 ppm, that will protect your chlorine longer from breakdown by sunlight, but the chlorine will still break down. You'd have to use algaecide weekly or a phosphate remover or maintain an FC level of around 6 ppm minimum to prevent algae growth (with the algaecide or phosphate remover, the FC can be lower). Perhaps you could go 3 days between chlorine additions, but if you wanted to add chlorine only once a week, you'd have to have significant swings in chlorine. The only way to avoid this is with a pool cover or an automatic dosing system (for example, The Liquidator). Unfortunately, there is no slow-release form of chlorine that doesn't add something else. Trichlor adds CYA and the slow-release Cal-Hypo tabs add to Calcium Hardness (CH) and also tend to break down quickly near the end (when they're small) and leave some residue (binders).

CYA is fairly evenly distributed in the pool water. People have measured it at various depths and it is NOT stronger at the surface or at depths. It is fully dissolved and just like any other dissolved chemicals, the concentration is the same throughout, especially with regular circulation.

If you use an algaecide (at extra cost), then you can operate with a lower FC and higher CYA which will use less chlorine daily. So you will still build up CYA, but perhaps not as quickly. If you can get your chlorine usage down to 1 ppm FC per day, then this builds up CYA at 18 ppm in a month so would require an 18% dilution of the water (almost 10" if average pool depth is 4.5 feet) every month to keep the CYA at 80 ppm. That's still a lot of water to replace regularly. In my own pool 6 years ago, my CYA went from 30 ppm to 150 ppm in 11 "in-season" months (over 1-1/2 years) and I only had a very low 0.8 ppm FC per day chlorine usage with an opaque pool cover and a cartridge filter. I switched to using 12.5% chlorinating liquid after that and add it twice a week -- no big deal and my chemical cost is only around $15 per month for a 16,000 gallon pool.

Richard

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Ok I think I starting to get it. I am gunna give LC a try and buy The Liquidator. Does anyone know where I can actually buy one?

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Ok I think I starting to get it. I am gunna give LC a try and buy The Liquidator. Does anyone know where I can actually buy one?

You can read more about The Liquidator and where to purchase it here. Note that it works well for some people, but for others it builds up calcium carbonate scale at its output valve assembly. It is possible that using 50 ppm Borates in the water can help prevent the pH rise (especially locally in The Liquidator itself) that makes this problem worse. Also, you will still need to buy and carry chlorinating liquid (or bleach) home to refill it.

The main reason that saltwater chlorine generator (SWG) pools are so common these days is that you don't have to add any chlorine (since it's generated using salt from the pool water) so they are less maintenance. They have their own issues, but most can be mitigated.

Richard

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Richard thx ALOT for all your help. I have been fighting this CYA build up for years. Its driving me insane.

I know I asked this before but can you give me a basic answer on this (i am an idiot when it comes to pool chemistry)

If I add LC myself cant I just maintain a proper level of stabilizer (by adding it) and not have to add the LC every day? If I dont buy The Liquidator that is.

THX!

Mark

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