Ph Level Climbs Every Day

[itabb]

Going back to the beginning of this thread when we started with reducing the TA, why does the PH have to be dropped to 7? Why couldn't I aerate between 7.3 and 7.8? According to the spreadsheet, the TA will change each time I add acid to bring the PH down. Does the TA reduce more or faster between 6.8 and 7.2 than 7.2 and 7.6?

[chem geek]

Yes, the aeration is more effective at lower pH because at lower pH there is more literal dissolved carbon dioxide (the specific species -- not all carbonates) in the water -- that is, some of the bicarbonate is shifted towards carbonic acid and carbon dioxide when the pH is lower. That puts the pool even more out of equilibrium with the carbon dioxide in the air so the rate of outgassing is increased. The relative rate of outgassing can be seen in this chart and the numbers came from the "[H2CO3] (actual-normal)/normal" line way down the spreadsheet at around line #364. A number of 0 means equilibrium; negative numbers mean more carbon dioxide in the air than in the water; a number of 1 means twice as much carbon dioxide in the water as in the air and is used as the base rate for all other rates. So a number of 5 means the outgassing is 5 times faster than at 1. You can readily see from the chart that lower pH very rapidly increases the outgassing rate. It's just more efficient, but you can certainly lower TA at higher pH -- it just takes longer or requires more aeration to get the same speed of reduction.

You'll also note that for normal pH and TA ranges in all pools, there is ALWAYS outgassing of carbon dioxide since the pools are intentionally overcarbonated. It's just that outgassing is a slow process since only a portion of the pool water is in contact with the air (only the surface) and that surface tension inhibits the outgassing which is a physical process so still air will also slow that down. Splashing, aeration (forcing air bubbles into the water) and wind speed up the movement of carbon dioxide from the water into the air. SWG systems do a lot of aeration since the hydrogen gas bubbles they produce contain no carbon dioxide and are small bubbles with high surface area to volume ratios so can pull a lot of carbon dioxide out of the water quickly.

[waterbear]

Guys, remember, it's a pool! It ain't rocket science! Don't make it harder than it has to be to maintain it. Don't get so caught up in the theoretical stuff that you forget what you are after. A pool that is clear, clean, sanitary, and easy to care for! Here is some PRACTICAL advice that I have seen work time and again in SWG pools:

1. keep your salt level slightly on the high side

2. put your CYA toward the higher end of the SWG's suggested range.

3. Keep your FC between 3-5 ppm. If you have CC or algae at 3 ppm move it up a bit!

4. Keep your TA low, perpaps even lower than 80 ppm by a bit.

5. monitor your pH daily (or close to it) and keep it at close to 7.6 as possible, don't let it go up and down like a yo-yo (IMHO, THIS is the key to having a trouble free salt pool!)

6 adding borates helps in many ways.

7. If you get CC over .5 ppm and they don't go away on their own in a day or two then shock the pool with liquid chlorine or bleach to about 20 ppm and let the chlorine level drop to 10 ppm before going in the water.

This is actually based on a lot of Chemgeeks chemistry but you don't need to go crazy with the chemistry part of it. The idea is to enjoy your pool with the least amount of work, isn't it?

[itabb]

Sorry, waterbear, this is just far too interesting. Also, I appear to be having a problem with re-occuring CCs under .5. Sometimes it's there, sometimes it's not. I have been hovering around 6FC, with the aquarite at only 15% output, 6 hours a day. The pool is mostly used early in the morning or late enough in the evening which eliminates sun exposure. The weekend is a bit different, but then I run 9 hours instead. I only started having this problem with the CCs after adding 15ppm Borax. I am worried about going to 30ppm, though the problem may be that the CYA is 50 and not 80. I just don't know.

I read Chem Geeks discussion on CYA, and I understand the theory that if I kick my CYA up from 50 to 80, the SWG will theoretically produce more chlorine faster, though I may need a higher level overall. Also, I'd like to run my pool motor less, not more. If sun exposure is minimized, why wouldn't I want to run unstabilized or maybe even at just 10ppm CYA and keep my FC levels around 1-2, unless that causes a problem with the generation of chlorines. Based on what I read, I don't see much of a difference in half-life between 50 and 80, but I do see a significant difference in santizing power. The math does not appear to support a high CYA level, unless I am missing something.

[chem geek]

Experiments by Mark (mas985) starting on the second page of this thread seem to indicate that my theory about higher CYA levels making the SWG more efficient is wrong. Instead, it appears that the industry's charts on CYA retention are wrong and that CYA protects chlorine more than would be predicted by a blend of half-lives based on the different chemical species (chlorine unbound to CYA vs. chlorine bound to CYA). So if Mark's results are correct and occur in most pools, then a higher CYA level with a correspondingly higher FC level would in fact be better for lowering absolute chlorine loss from the sun and allow one to lower SWG output since the loss from sunlight would be dramatically reduced even accounting for the higher FC level.

Now in your situation, if your pool is covered when not in use and does not get a lot of sunlight, then the higher CYA level is not as worth it. Maintaining a higher FC level at a higher CYA level in your case probably wouldn't be wasteful since the FC loss should be similar in absolute amount (so similar SWG on-time) but it would be unnecessary. You could run at lower CYA and FC so long as your FC was enough to handle local consumption and imperfect circulation (usually 1-2 ppm minimum). The 3 ppm FC is already pretty low so having that at a lower CYA just gives you some extra safety against algae growth, including yellow/mustard algae.

Richard

[itabb]

I read that entire thread. Absolutely fascinating. So CYA does not impact FC production in the SWG, and PH is actually more of a factor. This would explain the FC behavior in my pool at PH 7.2 vs the current 7.8 levels.

I liked Mark's idea that he always runs the pump and SWG while in it. I'm going to try that out and see if that does not help with my burning eyes. When I was at 10ppm FC, 7.2-7.4PH and 0 Borates, no burn at all while the pump was off. Since adding Borates, I am at 7.8, 6FC, 15 Borates, and CCs keep showing up in the under .5 range. I'm going to guess that CCs are forming while the water sits and will clear within a certain amount of run time. I can probably predict that run time if I could figure out the rate at which all the water in the pool is circulated one time. Also, the PH at 7.2-7.4 was very stable. In fact, at 15% SWG output, PH seemed to edge downward, whereas at 50%, it rapidly moved up (measured after the FC returned to 10, as best as I could tell).

It could also be that I simply am not running enough hours. I run 4 hours during the day, with some flow impedance due to the solar panels. I run 2 hours in the middle of the night as well. We swim usually early in the morning and late in the afternoon, when the pump is done.

I'm going to go out on a limb and guess that the reason CCs were not present when we swam at 10FC and 0 Borates and 7.2 PH was due to the effective sanitation levels of a higher FC at a lower PH, even with the pump not running. I'd like to go to 70-80ppm CYA, but I am worried that 10FC will not be enough based on what I have seen so far. I'll have to think a bit before I commit to raising my CYA to 80.

One other observation based on the experiments in that thread. It seems the recommended CYA levels by SWG manufacturers is based on full sun exposure during the day. Is the recommended level different for indoor pools? Overall, it seems that if you have some or total sun exposure, a CYA of 80 has a cost savings over 50 in preserving chlorine vs levels for sanitation (which is not what that graph shows).

[chem geek]

It is reasonable that the high FC at lower pH combined with sun exposure broke down the CCs faster. The disinfecting chlorine level at a pH of 7.3 and FC of 10 is 0.11 (assuming CYA is 50 ppm) while at a pH of 7.8 and FC of 6 it is 0.05 or less than half. By the way, the effect of the pH change is rather small since CYA buffers the disinfecting chlorine so if you had kept the FC at 10 then at pH of 7.8 the disinfecting chlorine is 0.09 so less, but not as much as one might expect (say, compared to not having CYA where disinfecting chlorine would drop from 5.8 to 3.0).

Your experience with pH rise at higher SWG output is well understood at this point. That's just due to more outgassing from the hydrogen gas production in the SWG. The tiny hydrogen bubbles rather efficiently pull out the carbon dioxide out of the water and into the air which causes the pH to rise (with no change in TA).

Since SWG production is dependent on pH, and seemingly rather constant from 7.0 to 7.5 but then drops off from 7.5 to 8.0 (at least with Mark's SWG), it's a tough decision to make as to the proper pH level. At the lower pH of 7.5 one has more efficiency in the SWG so the lower setting (on-time) helps reduce pH rise, but the lower pH itself contributes to pH rise as shown in this chart. Mark reported a 15% reduction in SWG output (FC level) from 7.5 to 8.0, but the difference in outgassing rate at a TA of 100 between a pH of 7.5 and 8.0 is a factor of 5.8 so running at a higher pH is better IF it is needed to prevent a rise in pH. Clearly, a lower TA is better but mostly affects the amount of acid needed (which is proportional to the numbers in the previous chart) while the lessening in pH rise is much less dramatic as seen in this chart (remember these are relative, not absolute, rates of rise).

It is normally recommended by the industry that no CYA is to be used in indoor pools since there is no sunlight. However, that is, in my opinion, incorrect advice since the disinfecting chlorine levels will be far too high in such pools. That leads to much faster corrosion, ruining of swimsuits (my wife can attest to that during the winter when she uses an indoor pool vs. the summer in our own pool with no problems), faster creation of disinfection by-products, etc. I believe that some CYA, even 10-20 ppm, would be very beneficial in indoor pools. For indoor pools using an SWG, it is virtually imperative that CYA be used or else corrosion of stainless steel is quite rapid -- one user saw such corrosion in less than a year. Yet no one in the industry is recommending that. This is all part of the "CYA doesn't matter" philosophy pushed by manufacturers of CYA-based products (Trichlor, Dichlor) and not only causes many pools to get algae when the CYA gets high and the FC isn't raised accordingly, but it prevents sound reasoning from being applied to indoor pools causing greater rates of asthma and respiratory illness in competitive swimmers and small children -- all because the industry refuses to acknowledge the science behind the chlorine/CYA relationship ("it doesn't apply to REAL pools" is their standard line and they refer to a study which I discuss in this thread). I quite frankly don't know how these people sleep at night. Perhaps they only see their position simply generating profits from pools getting algae (and subsequent sale of algaecide; or preventing algae through regular sale of algaecide), but the negative impacts of the position are far worse, in my opinion. I have contacted some of these manufacturers and will continue to do so in the hope such positions will change (eventually).

Richard

[waterbear]

Sorry, waterbear, this is just far too interesting. Also, I appear to be having a problem with re-occuring CCs under .5. Sometimes it's there, sometimes it's not. I have been hovering around 6FC, with the aquarite at only 15% output, 6 hours a day. The pool is mostly used early in the morning or late enough in the evening which eliminates sun exposure. The weekend is a bit different, but then I run 9 hours instead. I only started having this problem with the CCs after adding 15ppm Borax. I am worried about going to 30ppm, though the problem may be that the CYA is 50 and not 80. I just don't know.

It's not the borates, it's the low cya and short pump run time. You are getting dead spots where the chlorine is burining off while the generator is not producing, it has nothing to do with the borates. It might also be an artifact left over from the overdose of ascorbic acid you put in. get your cya up another 20 ppm. bump your pump run time up so the genterator is producing chlorine in a more spread out time period and reduce the cell output if necessary and you will find your problem goes away.

I read Chem Geeks discussion on CYA, and I understand the theory that if I kick my CYA up from 50 to 80, the SWG will theoretically produce more chlorine faster, though I may need a higher level overall. Also, I'd like to run my pool motor less, not more. If sun exposure is minimized, why wouldn't I want to run unstabilized or maybe even at just 10ppm CYA and keep my FC levels around 1-2, unless that causes a problem with the generation of chlorines. Based on what I read, I don't see much of a difference in half-life between 50 and 80, but I do see a significant difference in santizing power. The math does not appear to support a high CYA level, unless I am missing something.

The theorectical stuff you and chem geek have been discussing is interesting but I am talking about real life experienc with many pools. My suggestions do not contridict what chem geek is telling your and he will be the first one to tell you that. Richard and I have collaborated on many things in the past!

When you are only running your pump for 6 hours you are not generating any chlorine for 18 hours. Several hours of that will be during daylight and you will be getting chlorine loss from UV. This can produce dead spots, nascent algae blooms begin, and CC forms. Borates in a 30-50 ppm concentration will help prevent this to some extennt but the real cure is to get the cya into proper range and toward the higher end is better than the lower and to run the pump longer with a lower cell output. This will spread the chlorine generated throughout the daylight hours better and help elimimate problems with local drops in FC level. I also told you to wait on the borates until you got the chlorine demand problem from the ascorbic acid under control. You didn't listen there either and I don't beleive that you have solved that problem yet! It can literally take a month to oxidize ascorbic acid added to a pool to remove staining when put in at normal dosages and you overdosed!

[chem geek]

Just to reiterate that just because we may now have a "different" explanation for why the high CYA levels may work (i.e. makes chlorine last longer even at proportionately higher levels vs. making the SWG more efficient) that doesn't change the result of higher CYA being more effective for many SWG pools in allowing less chlorine loss from sunlight and allowing lower SWG output and therefore reducing the pH rise. However, by having a more accurate technical explanation, we can more readily answer questions such as whether the higher CYA for SWG makes as much sense if a pool is not exposed to sun as much (due to a cover or due to being indoors). Your pool may fall into this category since it sounds like you keep it covered when not in use. Higher CYA will help when the pool is exposed to sun, but that may not be enough time to be that noticeable -- there's no way to know for sure except actual experiment in your pool.

As waterbear has indicated, we are almost always in agreement, mostly since we both look at the chemistry (or physics) involved but also trust in user's experiences and experiments and then modify the theory accordingly (as needed). As he says, his advice is not different than mine. I understand that your statement to waterbear was mostly just expressing your interest in the technical details.

Richard

[itabb]

I also told you to wait on the borates until you got the chlorine demand problem from the ascorbic acid under control. You didn't listen there either and I don't beleive that you have solved that problem yet! It can literally take a month to oxidize ascorbic acid added to a pool to remove staining when put in at normal dosages and you overdosed!

Nuts!

[itabb]

Temp 89

FC 7.5

TC 7.5

PH 7.7

Over 24 hours, 6 hours run time, cover on, used twice, generated positive 1ppm Chlorine and eliminated the .5 CC. Still a slight burn on the eyes, not as bad as yesterday.

I noticed on the spreadsheet that if I add 5 boxes of 20 mule team Borax, I also add 21ppm of total ammonia. If memory serves, the chlorine will attack the ammonia, often forming CCs. Is that right? Maybe that is the source of my organics and I just have not yet burned off all of the ammonia from the last borax treatment.

[chem geek]

Huh? I don't see how adding the Borax adds to ammonia. Are you sure you aren't misreading the line in the spreadsheet? It adds to the "Total Borate" line, not to the line below it which is "Total Ammonia". Borax does not add any ammonia. After it dissolves in water, it produces Boric Acid, sodium ion, hydroxyl ion, and water. This is equivalent to adding Boric Acid and lye / caustic soda / sodium hydroxide.

[itabb]

Maybe I have an old version or something. I swear, when I add Borax, it shows the amount difference in the next white column, and copies that to the row underneath, which is the ammount difference for Ammonia. Maybe you can post a link to your latest version?

[itabb]

Richard,

When using your spreadsheet to evaluate the impact of adding 20 mule team borax, I get different results if I add the borax, then add the acid, vs adding both together. Which is the correct simulation to apply considering I added 76 oz of borax followed immedately by 6 cups of acid?

[chem geek]

Richard,

When using your spreadsheet to evaluate the impact of adding 20 mule team borax, I get different results if I add the borax, then add the acid, vs adding both together. Which is the correct simulation to apply considering I added 76 oz of borax followed immedately by 6 cups of acid?

I fixed the bug regarding the borates "difference" showing up in ammonia and the fixed spreadsheet is in the normal location here. As for adding borax and acid separately vs. at the same time, here's what I get step by step:

pH 7.5

TA 100

Borates 0

I then set the Borates goal to 50 ppm and under the Borates section it says to add 588.7408 ounces weight of Borax (I set the Base to 20 Mule Team Borax earlier). I then enter that in and press the "Calculate pH/TA" button to get the following:

pH 8.93

TA 212.9

Borates 50

Without deleting my entry in the Borates section, I change the Goal pH to 7.5 and click on the "Calculate Acid/Base/TA" button to see 280.7767 for the required amount of acid (the TA in the Goal changes to 105.7). Clicking on "Calculate pH/TA" at this point doesn't change anything so entering a combination of 588.7408 ounces weight of Borax plus 280.7767 fluid ounces of Muriatic Acid results in:

pH 7.5

TA 105.7

Borates 50

If I now do this in two steps, the first step I already showed above (with the pH of 8.93) but if I then click on the new button "Set Initial = Goal and Clear All Inputs" (or manually copy the Goal to the Initial and clear all inputs) and enter 280.7767 for Muriatic Acid and then click on "Calculate pH/TA", I get the same result as above with a pH of 7.5, TA of 105.7 and Borates of 50.

Can you take a look at what you are doing again and see what's different than what I just did? You can also take the latest spreadsheet since the new button does make it easier to do the multi-step analysis.

Now let me do what you did. Starting with pH 7.5, TA 100, Borates 0 (CYA is 30), 76 ounces of Borax gives me:

pH 8.37

TA 114.8

Borates 6.45

If I copy the above from Goal to Initial and clear all inputs (that is, my borates entry) and then enter 6 cups of acid I get:

pH 7.27

TA 96.2

Borates 6.45

If instead I do both steps at once, I get the same as the above (the TA is 96.1 instead of 96.2 if I don't copy over the TDS that changes -- it's a minor effect -- if I copy over everything from Goal to Initial in the two-step method or use the new button to do that, then I get exactly the same result as above).

Richard

[itabb]

I'm working on progression, so my numbers are specific.

ph 7.17

ta 88.3

bor 18.12

Add 6 cups of muratic acid and 76 oz of Borax.

1 step:

ph 7.08

ta 85.7

bor 22.42

2 step

a. add 76 borax

ph 7.56

ta 98.2

bor 22.42

b. add 6 cups of acid

ph 7.08

ta 85.7

bor 22.42

Well, I see my imagination is quite active. I must have had inconsistant numbers somewhere. I even did a 3 step including CYA and it came out the same.