Cyanuric Acid Problem

[rbdeli]

I followed Richard's advise a year ago. My CYA was very high, causing me to need unreasonably high chlorine levels. The Puck chlorinator is now turned off permanently. I use liquid bleach exclusively. The pool store lady told me the same thing,

"Liquid bleach is too messy. It will raise your TDS levels" But she said nothing about the way her store products raised my CYA out of control.

Last year, I drained about 6 inches of my pool and refilled every 2 days for the entire last 2 months of the summer. The CYA is at a fairly reasonable amount now and I plan to lower it more this summer with more frequent drainings and refills.

Rob

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

[chem geek]

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

Mark,

The reason you need to add LC frequently isn't to add more stabilizer. As you point out, you can add that initially either using pure CYA or using Dichlor (or Trichlor tabs, though that takes too long) so your stabilizer level will be maintained even if you didn't add any LC. The reason for frequent LC addition is to get chlorine. With Trichlor tabs, they slowly release BOTH CYA and chlorine. That's why you don't need to add chlorine every day when using Trichlor -- the Trichlor is adding chlorine continuously as the tablets dissolve. Chlorine gets used up when exposed to sunlight and to bather load while CYA doesn't, but chlorine is what you have to have in the pool water to sanitize it.

Richard

[mark6437]

Rob, how are you adding the LC? With an automation system or by hand everyday?

Is it easy to mess up and add too much LC? I dont wanna gas my kids one day.

Thx

Mark

[Ari]

Hi Richard, thanks very much for your informative replies, I took your advice and bought the best (read most expensive ) Taylor kit, and have so far tested FC, PH, CYA, CH and TA. I find the CYA test a little imprecise as I don't know whether to stop adding the sample when the black dot is pretty much gone with just the faintest hint visible, or completely gone to where you cannot make it out at all. If completely gone, looks like im right around 50ppm, which I guess is pretty good, if it drops I'll use tabs for a few week to get it back in the 50-70 range?

It's interesting about the Ph test, prior to getting the taylor kit, my strips had seemingly been reading slightly low for PH these past few days, which I didn't fully believe as I have heard new pools tend to have higher Ph and need acid fairly often to lower it, and yet, my first liquid test today showed the ph to be slightly high, very different from what the strips were telling me, so, I added a little acid which brought it to a pretty ideal 7.4-5 or so.

Here's where I'm still a little confused though.

I added half a jug, ie. 1.25 gallons of 10.5% liquid chlorine a few days ago, and it brought my TC and FC levels very high, and, despite about 3 sunny days since, the FC is still reading very high. Since the Taylor kit only tests to 5ppm, I can tell you it's at least 5, looks like an even deeper pink than the max. of 5ppm, my strips are showing it might be as high as 10ppm. I did put 2 3" tabs in the in line a few days ago as well, but only set it to 2, I was wanting to keep some chlorine in the pool, since I was under the impressiuon the 1/2 jug of LC I added would dissapate in just a couple of days, but, here I am around 3 sunny days later, and the FC is still at least 5ppm, I do know that I should stop the tabs if and when the CYA level rises to maybe 70 or so.

So, here are my questions:

If my CYA level is hovering around 50, is it OK to add 1.25 gallons of LC maybe twice a week, even if my FC reads greater than 5 ppm for a day or 2, and I make sure it never falls below 3ppm? At what ppm should I add new chlorine? I know some literature says it can safely get as low as 1ppm, but it seems to me to be safe, 3ppm is a good minimum, what do you all think?

I would ideally like to add half a jug 2 times a week give or take, if this keeps my FC between 3 and 6ppm, is there any problem with this, with my CYA levels around 50-70?

Am I going to always have to add acid after I add LC? Most stores push muriatic, but one store guy said he prefers sulphuric?

Where should my TA be, right now it's 90ppm, sounds pretty good?

I know if my pH is slightly high, I can just add a cup or so of acid to bring it down, but what's the best thing to use to raise the pH without resorting to adding LC, since the FC might already be on the high side?

The strips say my TH is around 250, low side of normal, my Taylor says my CH is about 220 ppm, should I maybe shock with 2 lbs/ (15,000 gallons) cal-hypo once every 2 weeks until the Ch gets to maybe 250 or so? Where exactly should my Ch be, and, what's the best way to get it there? Is there any reason to NOT add calcium to a 6 month old pool?

I'm sorry for all the questions, my first pool, don't want to do anything wrong , and I feel like I'm getting there, I've only been caring for it myself for a few weeks, and now that I have an accurate test kit, I feel like I'll be OK very soon, but any and all info pertaining to the above questions would really help, and is much appreciated!

Ari

[chem geek]

Ari,

You should view the CYA test outdoors with the sun behind you so that you shade the tube with your body (if it's overcast, then it doesn't matter). Take a look at the pictures in this link to get an idea of what to look for in terms of the black dot disappearing. It should not be visible, but if you think you can't see it but are not sure, that's probably where to stop (if you add more liquid to the tube and it doesn't appear to change, then you did indeed go far enough).

Since your chlorine kit will only measure to 5 ppm, it sounds like you got the Taylor K-2005 which is NOT the one I recommend. If you've read the posts on this forum, you would see that what is recommended is the Taylor K-2006 test kit 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 is less expensive "per test". Since you've already got the K-2005, you can just get the FAS-DPD chlorine test here. This FAS-DPD test will measure accurately to within 0.2 ppm and can measure up to 50 ppm.

Test strips are not usually accurate and they can't measure Calcium Hardness (they only measure Total Hardness). I would trust the pH in your Taylor kit. You are correct that new plaster curing makes the pH rise as well as increasing the CH somewhat, but after 6 months this has probably slowed down significantly. You may still notice it up to a year, but it's the first months that are the most extreme.

As for what level of chlorine to maintain, you can look at the Chlorine / CYA Chart at the Pool School and should just read the Pool School articles to learn how to maintain your pool. If you have a pool cover, then you can usually just add chlorine twice a week, but without a pool cover you usually have to add chlorine every day or two. It's possible you only have to add it twice a week, but usually sunlight will break down the chlorine faster than that unless the CYA is higher (70-80 ppm) in which case you need to maintain a higher FC level to prevent algae growth.

If you wanted to have a lower FC level and use less chlorine, then you could add a supplemental algaecide (PolyQuat 60) weekly or use a phosphate remover, both at extra cost, to prevent algae, though as I said if you maintain the proper FC/CYA ratio then you can prevent algae growth using chlorine alone.

You can use The Pool Calculator to figure out dosing and to calculate the saturation index which will tell you if you need to adjust CH or other parameters. The saturation index is a little low so you could raise the CH to 300-350 ppm, but if your plaster is still curing then the CH may go up a little anyway. Also, remember that evaporation and refill will increase the TA and CH in your pool over time because the TA and CH in your fill water get added to that in the pool (evaporation only removes water).

Richard

[Ari]

Hi Richard, when you said I can keep my pH stable by lowering TA, how low is low? Right now, it's hovering around 80-90, and it seems to be actually getting lower over time, definitely doesn't appear to be going up, though I would guess it will rise a bit when I add some more LC, since the pH is around 13?

Do the periodic additions of acid to lower pH also lower TA in a meaningful, lasting way? I do find I need to add a little acid every day or 2 to keep the pH at the 7.4-7.6 range.

Would you say I should get my TA up to maybe 100 or so?

Also, most pool stores and most people seem to suggest muriatic acid for pH control, but one pool store suggests sulfuric, any thoughts on that?

Thanks, Ari

[chem geek]

Ari,

When adding chlorinating liquid or bleach the pH rises upon addition, but it falls again after the chlorine is consumed since that is an acidic process. It is close to pH neutral over time IF the TA isn't too high. The TA should only be getting lower if you are adding acid to the pool, including use of Trichlor (or Dichlor) which is net acidic.

If you need to add acid every day or two to keep the pH from rising too much, then your TA is too high. Let it drop to 70 ppm as it will over time from acid addition and see how that works for you. If necessary for a plaster pool, you can raise the CH level to keep the saturation index near zero.

Do NOT raise your TA when your pool's pH tends to rise over time. The higher TA will only make that problem worse. Also, you can target a slightly higher pH range of 7.5 to 7.7 instead of 7.4 to 7.6 which should also help reduce the rate of pH rise.

Muriatic Acid is better because it does not add sulfates to the pool -- it only adds chloride. Dry acid (sodium bisulfate) and sulfuric acid both add to sulfates -- not a horrible thing but higher sulfates plus the magnesium in the pool can be harsh on stone and cement since magnesium sulfate has extremely high salt recrystallization pressure.

Richard

[Ari]

Ari,

When adding chlorinating liquid or bleach the pH rises upon addition, but it falls again after the chlorine is consumed since that is an acidic process. It is close to pH neutral over time IF the TA isn't too high. The TA should only be getting lower if you are adding acid to the pool, including use of Trichlor (or Dichlor) which is net acidic.

If you need to add acid every day or two to keep the pH from rising too much, then your TA is too high. Let it drop to 70 ppm as it will over time from acid addition and see how that works for you. If necessary for a plaster pool, you can raise the CH level to keep the saturation index near zero.

Do NOT raise your TA when your pool's pH tends to rise over time. The higher TA will only make that problem worse. Also, you can target a slightly higher pH range of 7.5 to 7.7 instead of 7.4 to 7.6 which should also help reduce the rate of pH rise.

Muriatic Acid is better because it does not add sulfates to the pool -- it only adds chloride. Dry acid (sodium bisulfate) and sulfuric acid both add to sulfates -- not a horrible thing but higher sulfates plus the magnesium in the pool can be harsh on stone and cement since magnesium sulfate has extremely high salt recrystallization pressure.

Richard

Hi Richard, once again thank you for your vast experience and willingness to help out us newbies, so we may take good care of our considerable aquatic investments.

Now, I think I'm on the verge of understanding at least some of this, then again, I've been on the verge before, but sometimes only of looking foolish, so, let's see which one it is this time.

TA from what I've been reading is usually said to be good in the 80 to 120 range, mine was between 80 and 90, at the low side of normal. You said that if I'm seeing the ph rising consistantly, I should lower the TA to maybe 70 or so, and I can compensate by upping the CH a bit, right now, CH is at 220, maybe get it to 250? Then again, keep in mind the pool was finished only 4-5 months back, so, I expect the pool to at least add a little more CH (and other alkaline substances) to the water in time, and don't new pools tend to cause the ph to rise for a while until they're broken in so to speak? Is it that my TA is too high, or is it the new pool syndrome raising the ph, or, it is what it is?

EDITED TO ADD: As I have been reading, aside from my plaster pool being newish, I also run my pump, and 3 spills a lot, maybe on average 12 hours a day, and apparently, this aeration is contributing to my ph rising a bit each day? Another reason to lower TA to 70 and see if the ph is more stable?

Richard, are you saying that if I lower my TA to 70, instead of needing to add acid every 3 days or so to stay in the 7.4-7.6 range, I might only need to add acid once a week or even once every 2 weeks, is this possible just by lowering TA 10-20 ppm?

Is the following correct?

Your ph, in part, is the result of a battle, or stasis, between the very low ph of the acid you add periodically, and the alkaline substances you add, or are added by your pool/elements, ie plaster, rain, tap water, etc.

When you add LC, though it's high ph does make the water temporarily more alkaline with a rise in ph, it is only temporary, the long term TA and ph are relatively unaffected by the periodic additions of LC, is that true for the most part? So, for example, if you want or need to add LC, you can add it, even if your ph is already 7.6, and you do see a spike in ph, to maybe 7.8 or so? Or, if you do, should you add acid anyway to bring it down to 7.5, or just wait a day or 2 for it to happen naturally? How long does a LC ph rise last, and could it last long enough to damage the pool, with a high ph?

While the temp. ph and alkalinity rise you get when you add LC is short lived, when you add acid to lower ph, does that acid stay active in the water long term, unlike LC, in other words, as you add the acid over time, does it build up and stay in the water as a ph and alkalinity reducer, or, like LC, does the acid only lower ph and alkalinity temporarily? Is is fair to say you have to keep adding LC because the sun (and contaminants) consume it, but, you have to keep adding acid not because it gets consumed, but because the pool, and the elements are constantly adding alkaline substances which are what's raising your ph over time, and the acid is required to counteract this?

Why would my pool need a lower than normal TA, is it because it being a new pool, there are a lot of substances it's giving to the water that are adding to TA and thus raising ph? If true, then as my pool gets some time behind it, I would see the ph start to not rise as much, which means my TA is naturally lower and not increasing, and then I could bring it up with SB to a middle range of say 100 or so?

I recall the pool company saying that new pools do tend to have high ph for a while, the impression I got from them was I should just add acid as neccessary to keep the ph in the correct range and that in time, the ph of the water would not rise as much or as quickly. I also had the impression, which I'm now thinking was false, based on what you're saying, that you add acid to compensate for the ph rise the LC gives, when if I now understand correctly, the acid you add isn't really about the LC, but rather because your pool is giving off alkaline (high ph) substances that are raising TA and PH, is this true?

So, is lowering my TA as you suggested, in effect, a temp. measure to compensate for my newish pool adding things to the water that are raising the TA naturally, and thus the ph rises quickly? How are TA and PH related exactly, maybe that's where I'm not quite getting this. Does more CH in the water act like TA as an acid neutralizer/buffer and ph stabilizer? Is that why you said if i lower my TA, I could add calcium to compensate, does the calcium act just like TA, as an acid/ph buffer? What's the ph of calcium?

And finally, if I can keep my TA right around 80-90, my CH around 250, my FC around 5-6, my CYA around 50 and my ph right in the 7.4-7.6 range, aside from the added expense of paying for a little extra acid, is there anything dangerous for the pool if the only issue is I have to add some acid every 2-3 days to keep the ph between 7.4-7.6?

I'm sorry for so many questions, I do read lots of posts, and other info on the net, but, little of it helps me as much as having my questions answered directly, I hope you can bear with me, I think i'm pretty close to getting a handle on it all, and thus I expect the questions will dissapate faster than unstabilized LC in the sun.

[txpoolguy]

I really hesitated to stick my nose into this conversation, as I can admit, my eyes are starting to roll back in my head, but I can imagine how it hits the avg. homeowner. Collectively, our goal is to help the pool owners keep their pools in good shape for the least amount of effort possible. All of the comments above are solid and I would not take anything from them. If I'm repeating what's been said already, I do beg your pardon.

Having been in the pool industry in multiple aspects for 25+ years (cleaning, service, building, mfg, service, service, etc., I find that although the principles of chemistry will always be the same, there are some necessary differences, geographically, in the application of the principles.

IMHO, in Texas, it's far more demanding on the consumer to try to maintain good water chemistry (and no algae) without CYA and without stabilized chlorine. In pools with a FC of 2.0, pH of 7.4, TA of 90ppm, you will still grow algae, period. Having worked with chlorine, bromine, ECG, etc., the CYA increase is a factor that we simply deal with because it's easier and cheaper than the alternatives. Large (300-500 sq. ft.) cartridge filters have become more popular (probably 60+% of new construction). There is not as much normal dilution, although often pool are built with "overflows" so rainwater does dilute the water as well. This is a factor, usually in the spring rainy season. and is a factor with salt levels for ECG as well. While draining the pool partially is not desirable, it is not wholly undesirable either. It is simply another way of achieving dilution, and does not have to be painful. I suspect that Mark may have low bather load, no overflow, and wih the cart. filter, has no normal way to dilute. Keep in mind, that draining the pool partially once per year, is likely replacing less water than backwashing throughout that same year, but will have the same diluting effect.

I've become a believer in phospate removers, not as a magic bullet, but as a major factor in controlling algae, since algae growth is usually followed by undesirable & expensive large doses of chlorine. We have huge and consistent phosphate levels in Texas, and south Texas is worse than N. Texas where I live. Since we work heavily with ECG now, I've seen the PRs make a night & day difference in ease of maintenance, for both salt users and non. Maintenance dosages are very good, and often the PRs are cheaper and more effective than algaecides, per dose and are certainly less expensive than chlorine. I can't imagine trying to maintain my personal pool with unstabilized CL. The biggest reason that liquid chlorine is rarely used in Texas is specifically because it's unstabilized.

Again IMHO, Trichlor tabs, cal hypo shock, muriatic acid and phospate remover is the way to go, or an ECG to replace the Trichlor and Calhypo. I may have to dilute the CYA and CH once every 12-15 months, but it's just not that hard.

Again, I do not wish to undermine any of your responses, as your education outweighs mine, but I think sometimes we get too deep for our audience?

[mark6437]

I really hesitated to stick my nose into this conversation, as I can admit, my eyes are starting to roll back in my head, but I can imagine how it hits the avg. homeowner. Collectively, our goal is to help the pool owners keep their pools in good shape for the least amount of effort possible. All of the comments above are solid and I would not take anything from them. If I'm repeating what's been said already, I do beg your pardon.

Having been in the pool industry in multiple aspects for 25+ years (cleaning, service, building, mfg, service, service, etc., I find that although the principles of chemistry will always be the same, there are some necessary differences, geographically, in the application of the principles.

IMHO, in Texas, it's far more demanding on the consumer to try to maintain good water chemistry (and no algae) without CYA and without stabilized chlorine. In pools with a FC of 2.0, pH of 7.4, TA of 90ppm, you will still grow algae, period. Having worked with chlorine, bromine, ECG, etc., the CYA increase is a factor that we simply deal with because it's easier and cheaper than the alternatives. Large (300-500 sq. ft.) cartridge filters have become more popular (probably 60+% of new construction). There is not as much normal dilution, although often pool are built with "overflows" so rainwater does dilute the water as well. This is a factor, usually in the spring rainy season. and is a factor with salt levels for ECG as well. While draining the pool partially is not desirable, it is not wholly undesirable either. It is simply another way of achieving dilution, and does not have to be painful. I suspect that Mark may have low bather load, no overflow, and wih the cart. filter, has no normal way to dilute. Keep in mind, that draining the pool partially once per year, is likely replacing less water than backwashing throughout that same year, but will have the same diluting effect.

I've become a believer in phospate removers, not as a magic bullet, but as a major factor in controlling algae, since algae growth is usually followed by undesirable & expensive large doses of chlorine. We have huge and consistent phosphate levels in Texas, and south Texas is worse than N. Texas where I live. Since we work heavily with ECG now, I've seen the PRs make a night & day difference in ease of maintenance, for both salt users and non. Maintenance dosages are very good, and often the PRs are cheaper and more effective than algaecides, per dose and are certainly less expensive than chlorine. I can't imagine trying to maintain my personal pool with unstabilized CL. The biggest reason that liquid chlorine is rarely used in Texas is specifically because it's unstabilized.

Again IMHO, Trichlor tabs, cal hypo shock, muriatic acid and phospate remover is the way to go, or an ECG to replace the Trichlor and Calhypo. I may have to dilute the CYA and CH once every 12-15 months, but it's just not that hard.

Again, I do not wish to undermine any of your responses, as your education outweighs mine, but I think sometimes we get too deep for our audience?

I agree with what you are saying but, I have to drain my pool every 3 to 4 months. Not 12. Right now I am sitting at 80ppm CYA. I was at 100ppm. I did a half drain and I am only down to 80ppm. I will be back up to 100ppm or more in no time. I am looking for a wy to fix this problem permanently. I do not know what that is yet. Dumping a gallon or so of LC in my pool everyday is not what I wanna do though. I may get a SWG but I am just not sure yet.

Mark

[PaulR]

I was at 100ppm. I did a half drain and I am only down to 80ppm.

If it was really a half drain, then you were at 160 not 100. The usual test doesn't go higher than 100, you could have 300 and it would look like 100.

The way to keep CYA from increasing is never ever add stabilizer or stabilized chlorine. Bleach or liquid chlorine only. The stabilizer doesn't go away or get used up; it's there essentially permanently.

--paulr

[Dr. Hot Tub]

Does anyone by chance have any links or info on what a high CYA level does to Liver function?

[chem geek]

Ari,

Thanks for reminding me that your pool was freshly plastered only 3-4 months ago. Yes, that probably means your plaster is still curing somewhat and that means that the Calcium Hardness (CH) and pH will rise since curing adds calcium hydroxide into the pool. At typical pool conditions with a TA at 80 ppm, a 10 ppm increase in CH from curing would have the pH rise from 7.5 to 8.4 (you would add acid before letting it get that far). So the rise in CH is slower to see than the pH, but would be noticeable over time. Curing is greatest in the first weeks and months and slows down rapidly in that timeframe, but may still be noticeable up to a year, sometimes a little bit up to two (after that, it still is curing but is so slow that it isn't a noticeable factor). In this situation, lowering the TA too much would make the pH less stable so most likely you wouldn't lower below around 80 ppm at this point and would just deal with having to add acid fairly regularly to control pH. Adding 50 ppm Borates to the pool is an option for having another pH buffer in which case you could have the TA lower, to 60 or 70 ppm, but with a higher CH to compensate. See The Pool Calculator to calculate dosing and the saturation index which you want roughly near zero.

You are absolutely right about your increases aeration making the pH problem worse and that a lower TA would help. So perhaps going the Borates route is your best bet since long term you do have a pH rising tendency and the use of Borates can let you safely have a rather low TA (again, compensating with a higher CH to have the saturation index be near zero). Just note that if you have a lot of evaporation and refill and your fill water is high in TA, then it can be hard to keep the TA low without use of a pool cover (and if you had a pool cover then the need for a lower TA is lessened in the first place). Just keep in mind that there isn't a single TA level "answer" for everyone -- just remember that if the pool tends to have the pH rise over time then a lower TA can help reduce that because TA is not just a pH buffer but a SOURCE of rising pH itself from carbon dioxide outgassing. This outgassing effect, with its pH rise, is worse at lower pH, higher TA and with greater aeration.

You do NOT lower the TA to 10-20. I'd never go below 50 ppm and we've never seen a single pool need anything lower than that even under extreme aeration conditions. For plaster pools you want to saturate the water with calcium carbonate so you do want some TA in the water. Though you can balance the lower TA with a higher CH, things get pretty whacky if you get the TA so low since 1) the pH buffering is very low (unless you also use borates) and 2) there is too much sensitivity to small TA changes and 3) about 1/3rd of the CYA level (at pH 7.5) contributes to TA with the rest being mostly bicarbonate. Also keep in mind that the "lower TA" is only appropriate when using net-pH-neutral sources of chlorine, specifically the hypochlorites (bleach, chlorinating liquid, Cal-Hypo, lithium hypochlorite). With net-acidic sources of chlorine such as Trichlor and Dichlor, you need a higher TA so that the outgassing effect counteracts the acidity from the net chlorine usage so that the pH is roughly stable.

Your analysis is correct about the hypochlorite sources of chlorine (including LC -- bleach and chlorinating liquid). If you have your TA set right (i.e. not too high), then over time the pH and TA are both stable. If there is a lot of evaporation and refill, then the TA and CH will rise from whatever is in the fill water since evaporation only removes water and nothing else. If there is water dilution from regular backwashing, then everything gets diluted down towards the levels in the fill water. The pH in my pool is very stable. The TA slowly rises over an entire summer season due to some evaporation and refill (in spite of a pool cover -- the pool is used every day for 1-2 hours). As for how long the pH rise lasts from the chlorine addition, it is directly related to the change in FC level so depends on how long the FC is higher. If I use an example of 70 ppm TA with 30 ppm CYA and no Borates, then if I increase the FC by 4 ppm, the pH rises from 7.5 to 7.73. as the FC drops back down, the pH drops as well. So you don't try and fight such small pH changes and let things naturally settle out. You only add acid for the "trend" if the pH is rising. Just measure the pH when the FC is at roughly the same level as that is easiest.

Just note that some bleaches and chlorinating liquid have more "excess lye" than others so would be an additional source of a slow pH rise over time. Clorox Regular bleach has the smallest amount of excess lye making essentially no additional pH rise effect. Off-brand Ultra bleaches have much more excess lye and most chlorinating liquid is in between. These effects are on the order of a 0.1 pH rise over 1-4 weeks (with no borates), depending on daily FC usage so not huge.

The pH rise effect from LC is temporary only because the added LC itself is temporary. That is, the FC rise is temporary because sunlight breaks down chlorine and the chlorine also is oxidizing organics (especially in higher bather load pools -- in most residential pools open to the sun, its sunlight that consumes the most chlorine). The effect of acid is permanent. The rise in pH when using LC is almost all due to outgassing of carbon dioxide, except as you noted when a pool has curing plaster. There aren't very many "other" sources of rising pH unless you are explicitly adding such chemicals such as pH Up (sodium carbonate).

After your pool's curing settles down, I would NOT raise the TA to 100 as you suggest because the aeration from the spillovers would likely still have your pH rise over time if using LC. You would only have a higher TA if you were using acidic sources of chlorine (e.g. Trichlor tabs/pucks) in which case the TA would likely need to be 120 ppm or more (and the CH a little lower to have the saturation index be near zero).

So, lowering the TA helps reduce the rate of pH rise from outgassing of carbon dioxide. It does not help the pH rise from curing plaster, though a very high TA would simply add to the effect of rising pH making it worse. It's hard to say where the "sweet spot" is for TA when plaster is curing, but I'd say not to go above 80 ppm if you've got aeration. Just add acid to keep the pH in the normal range while plaster cures; there really isn't any way around that. Even using borates will slow down the rate of pH rise, but it won't reduce the amount of acid needed per time -- it just changes from many smaller acid additions to less frequent larger acid additions.

CH has nothing to do with pH or TA. The only reason I brought up CH relative to lowering TA was for the saturation index so that the water remains saturated with calcium carbonate. The reason this is done is to protected plaster surfaces so they don't dissolve since calcium carbonate would otherwise dissolve in water. Pool plaster is partly made from limestone which is calcium carbonate, and even the harder calcium silicates that are formed after curing are affected by the calcium level in the pool. So long as you keep the saturation index near zero, there is nothing "dangerous" in the pool -- but your example numbers have a saturation index of around -0.2 which isn't horrible, but you might as well shoot for a CH of 350 ppm long-term if that's the TA level you will consistently have.

Feel free to ask whatever you like. That's the purpose of these forums -- to share information.

Richard

[chem geek]

txpoolguy,

I agree with you that most people don't care about the chemistry and just want to know, simply, what to do with their pools. However, others are curious or want more detail. Those that don't want to read a post with detail can just skip it.

I think you may have a misunderstanding because no one is saying to use unstabilized chlorine and have no or very low CYA in the water. In very hot climates with lots of direct sunlight such as parts of Texas and desert areas like Arizona, one can certainly use a higher CYA level of 80 ppm to protect the chlorine from more rapid breakdown in sunlight. In fact, there is one pool service in such areas (Texas, Arizona, Nevada, southern Calif.) that has the CYA at 100 ppm in their serviced pools and adds chlorine weekly going to 14 ppm. With the high CYA, the FC drops slowly to 3-5 ppm after a week. They use either chlorinating liquid or chlorine gas or a combination as their source of chlorine and none of their thousands of serviced pools get algae. They don't use any supplemental algaecides or phosphate remover. I'm not saying this is a great approach (though it does work) and if someone really wanted to do this then I'd recommend using 50 ppm Borates to keep the pH swings to a minimum, but it is a practical way to go if only servicing a pool once a week.

In other words, you can increase the CYA level in new water separately from the issue of using Trichlor vs. chlorinating liquid. Just because one uses chorinating liquid does not mean they can't have higher CYA levels in the water. You just have to be sure to not let the FC drop too low. It's ONE approach -- not the ONLY approach. What you mention, using a phosphate remover, is another approach where you don't care about the CYA level, though going way above 100 ppm will slow down oxidation of organics in the pool to the point where one would need to either shock the pool with higher FC (if not maintaining a higher FC overall) or use a non-chlorine shock to supplement oxidation. It sounds like you deal with this via dilution to keep the CYA in check.

In my own pool 6 years ago, I used Trichlor pucks in a floating feeder and my CYA rose from 30 to 150 ppm in 1-1/2 seasons (11 months of "in-season" use). My daily FC usage was low at around 0.7-0.8 ppm per day and I have an opaque electric safety cover. I also have a cartridge filter. So it doesn't take long for the CYA to rise. I was even using PolyQuat 60 algaecide, but only every other week. My pool started to get a higher chlorine demand which made it harder to keep up with the chlorine tabs. The pool started to turn dull. I was getting a nascent algae bloom, though no one at multiple pool stores knew what was going on, though had many suggestions for extra chemicals to help out -- from clarifiers, to shock, etc. That's when I decided to figure out pool water chemistry since chem/physics was my major in college.

I now use only 12.5% chlorinating liquid from my local pool store. They charge a decent price and they reuse the gallon bottles which is better than recycling. For my 16,000 gallon pool and around 1 ppm FC daily usage, this costs me around $15 per month. That's it. I add a small amount of acid about once every month or two. With my pool cover, I'm able to add chlorine just twice a week. It doesn't get much cheaper or simpler than that. And my pool has 2000-3000 ppb phosphates and my fill water has 300-500 ppb phosphates and fertilized soil gets into the pool at times (in spite of the cover -- comes in at the slightly open edge when the gardeners work). I just this year added 50 ppm Borates so will see if the chlorine usage drops at all (from the borates being a mild algaecide) and if the pool is better protected against algae if the chlorine drops too low. With a "well fertilized" pool, such as mine, it's pretty unforgiving if the chlorine gets too low (FC < 5% of CYA). I didn't have a single problem for years, but this year upon opening I didn't add enough chlorine as the water warmed up (I waited a full week) and got soil bacteria to convert the CYA into ammonia in a matter of days and that took a lot of chlorine to "fix". So having supplemental algaecide, borates, or phosphate remover should slow down or prevent that sort of situation -- we'll see at the end of this season when I'll do an experiment intentionally letting the chlorine get to zero and seeing how long it takes for things to start going wrong now that I've got borates in the water.

I now dilute the water with winter rains (after a few years of not doing that to see what around 1800 ppm salt levels were like) and I agree with you that this is good to do. I do this to keep the salt level down (to around 800-1200 ppm), but also to refresh the water since not all chemicals break down with chlorine or even with non-chlorine shock.

Bottom line, what you describe is another approach and I don't disagree with it working. But if one wants to minimize the amount of needed water replacement, then one can do that by not using so much stabilized chlorine. For some this works out OK, but I agree that without automation of chlorine addition, it's not as easy as having Trichlor pucks in a floating feeder or inline chlorinator. A saltwater chlorine generator (SWG) pool is easiest, but has its own issues that need to be mitigated that I won't get into here.

Richard

[chem geek]

Does anyone by chance have any links or info on what a high CYA level does to Liver function?

This link gives the info you are looking for, but basically skin absorption is minimal (5 µg/kg/day) and levels for first symptoms is pretty high (600 mg/kg/day). You couldn't even drink enough pool water high in CYA to get the daily amount to see any effects.

[Dr. Hot Tub]

Does anyone by chance have any links or info on what a high CYA level does to Liver function?

This link gives the info you are looking for, but basically skin absorption is minimal (5 µg/kg/day) and levels for first symptoms is pretty high (600 mg/kg/day). You couldn't even drink enough pool water high in CYA to get the daily amount to see any effects.

Thanks.. I have new computer and lost all of my data. There are a few other medical studies going on and I have not relocated them. Thanks for the new link.