Which Chemical Balance To Use?

[smallpooldad]

I have always maintained my pool at a CYA of between 30 and 35 (15 years), recentlly I have experimented with 40. I have not had issues with algae but I do use a fair amount of acid. However I was considering moving the CYA to 70 and running the chlorine at 4, as is often recommended on this site.

The pool is 10,000 gals SWG with an automatic acid feed pump. Below I list the current setup and a possible future setup. My only concern in the future setup is that the pool might become too acidic based on the "PoolEquations" Excel spreadsheet. Because of iron issues I like to keep the pH at 7.4, 7.5 as we have very soft nearly pure water (except for iron) in Honolulu does seem to allow the iron to precipitate, so I raised the Alkalinity in the "proposed" example to 100 otherwise the Calcite Saturation Index (CSI) would be -0.36.

Which setup would those of you in the know prefer, one thing to consider is that I beleive that moving from 30-40 CYA to 70 CYA is most beneficial for deep pools but my pool is only 4ft 6in deep at its deepest point so maybe it is not worth changing, so should I leave it where it is or change it. I would hate to drain it. I think the responders when I say "those in the know" would persons with a strong working knowledge of chemistry or persons who have shallow pools like myself and run their CYA at 70, as deep water pools are essentially another animal. This way I would receive real life experiences that are appropriate to my situation. One other thing to bear in mind is that UV index here is much higher in most months than in most of the mainland US, although we have less daylight hours in the summer and more than most the other half of the year.

Any help would be appreciated. Would there really be any benefit and would outgassing be an issue?

Using "PoolEquations" Excel spreadsheet results:

Current:


Measured pH 7.4
Total Alkalinity (ppm CaCO3) 90
Free Chlorine (ppm Cl2) 4.0
Cyanuric Acid (ppm CYA) 40
Calcium Hardness (ppm CaCO3) 375
Total Dissolved Solids (ppm) 3300.0000
Total Sulfate (ppm SO42-) 0
Total Borate (ppm Boron) 0.0
Total Ammonia (ppm Nitrogen) 0.0
U.S. Gallons 10,000
Temperature (oF) 84

Total Chloride (ppm NaCl) 3127
Carbonate Alkalinity (ppm CaCO3) 76.9
Langelier Saturation Index (LSI) -0.11
% HOCl (vs. Total Free Chlorine) 1.1%
OCl- (as ppm Cl2) 0.043
HOCl (as ppm Cl2) 0.043
Calcite Saturation Level (CSL) 0.59
Calcite Saturation Index (CSI) -0.23



Proposed:


Initial
Measured pH 7.4
Total Alkalinity (ppm CaCO3) 100
Free Chlorine (ppm Cl2) 4.0
Cyanuric Acid (ppm CYA) 70
Calcium Hardness (ppm CaCO3) 375
Total Dissolved Solids (ppm) 3300.0000
Total Sulfate (ppm SO42-) 0
Total Borate (ppm Boron) 0.0
Total Ammonia (ppm Nitrogen) 0.0
U.S. Gallons 10,000
Temperature (oF) 84

Total Chloride (ppm NaCl) 3092
Carbonate Alkalinity (ppm CaCO3) 77.6
Langelier Saturation Index (LSI) -0.10
% HOCl (vs. Total Free Chlorine) 0.6%
OCl- (as ppm Cl2) 0.023
HOCl (as ppm Cl2) 0.023
Calcite Saturation Level (CSL) 0.59
Calcite Saturation Index (CSI) -0.23

 

[JasonLion]

You seem to be mixing up some unrelated issues. Raising CYA has nothing to do with long term acidity. Adding CYA will lower the PH just a little, but then you raise it back up (or it goes up on it's own) and after that there are no further effects on the PH that have anything to do with CYA.

You also seem to be trying to micromanage everything, which is never a good idea. Many of these levels will change over time regardless of what you do. It is impractical to keep everything at very specific levels, instead you let the numbers vary through an acceptable range.

If you want to try out higher CYA levels, try something around 50 to start with and see how you like that, before going any higher. The main problem with CYA levels over 50 is that fighting algae becomes more and more difficult as the CYA level goes up.

 

[smallpooldad]

Jason Lion,

I am aware that CYA is not related to acidity levels, at least in any meaningful way. Maybe I did not make myself clear I was referring to further increasing my alkalinity level and would that be an issue when the site recommends 60 to 80.

But if raising it above CYA 50 might cause issues with algae, I think I will avoid raising the CYA as I would the plague and I thank you for that comment.

I do check the alkalkinity, twice a week, and the chlorine daily, so yes I suppose I micro manage a little, but then other than iron I have no issues.

But one question just for interests sake, based on our high UV index what level, a DEEP WATER SWG pool of say 20,000 gallons, and a CYA of 70, what Chlorine level would you recommend to guarantee no algae. This is what my neighbour has just done, so I am trying to help them out. They are using an Aquapure 1400 and the manual states that some pool association recommends not to raise the chlorine over 3, but use a CYA of 60-70. Does that sound right to you? It does not to me. And yes he does get algae issues as he is a little lax in his maintenance. I cannot count the times I have had to go over there and manage latent algae blooms as the pool gets cloudy, but he is in his late 70s and is convinced his pool equipment person knows more than I or this website, so I grim and bear it and gently persuade him to do as I say. Unfortunately his pool person told him to follow the manual so he just raised the CYA from 35 to 70.

Thank you for your quick reply it was very helpful. Come to think of it if it worked for me for 15 years why on earth do I want to go experimenting and micro managing you are right..

 

[JasonLion]

With CYA at 70 and a SWG, I would keep FC at between 3 and 5. In practice that means I would aim for 4, and expect it to vary a little and be 3, 4, or 5 at various times.

There are these old rules from before anyone used CYA that say to never let FC go above 3. When you don't have any CYA in the pool, that makes sense. Unfortunately, they have been copied over and over again, even though they don't really apply when there is CYA in the water.

 

[smallpooldad]

Jason Lion,

Once again thank you for the incredibly quick reply.

I will tell him 5 because I know he can let it go due to his lax ways. This number 5 will in all probability sound OK to him as I will explain this is barely above 3 and better than the 8 I would have recommended, need some Psychology here to make sure he thinks it is someone more knowledgable than I, which after all is true.

Very helpful,

Thank you.