Need to keep SWG pool at 7.4 - Is CH 600 too high?

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smallpooldad

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Aug 6, 2008
429
Honolulu
SWG plaster pool needs to be kept at a pH of 7.4, due to iron; 7.5 does not work it starts to precipitate, our water is very soft, not sure if that is why. I like the CYA at 30, works for me, those two numbers I will not change. I understand that the numbers will fluctute somewhat but here are the two sets of targets as starting points only.

One other point, I do not know whether or not it will make any difference, the pool will now recieve a weekly maintenance dose of Jack's Magic "The Purple Stuff".

I realize FC of 4-6 is somewhat high but we have one the highest incidences of antibiotic resistant flesh eating bacteria in the US, mostly from water, so in our case better safe than sorry. The doctor I visited informed me, if caught early enough, certain antibiotics, targeted for the specific strain, can be use to treat the infection. Cultures have to be taken and grown, if the culture does not grow it is hard for the doctor to know what to perscribe. This can happen if you are already on an antibiotic as I am. Well it seems my foot infection is getting better but still not going way, lab results will be in tommorow.

Which of these two setups would be better, if the pH needs to stay at 7.4 and the CYA at 30, you are welcome to make other recommendations? I show both the "Pool Calculator" for the CSI, and the "poolequations" spreadsheet of 1/10/2010, which gives a slightly more negative figure, not sure why.

Current and Proposed

FC 4-6 Same
pH 7.4 Same
TA 110 70(60 is where the water normally settles naturally but I can up that a bit or up the CH over 600)
CH 350 600
CYA 30 Same
Salt 3300 Same
Borate 10 Same (might go up to 50 if I can find some cheap Boric Acid - not Borax as I do not like adjusting the pH)
Temp 84F Same (goes to 78F in winter)
CSI "Pool Calculator" -0.12 Same
CSI "poolequations" spreadsheet" -0.15 Same
Carbonate Alkalinity (ppm CaCO3) from "poolequations" spreadsheet" 98.8 58.8

Is CH 600 too high, would it be detrimental in any way, could it be moved higher? Is the CSI too negative? The pool will lose TA naturally, will add CH as necessary until in balance, whatever that CH may be, based on your recommendations.

Thank you to those of you that might reply.
 
Thank you for your reply.

The main issue is that the the alkalinity will tend to naturally drift to 60ppm, and if that were to occur the CSI with a recommended max CH of 350 in a SWG plaster pool would be be -0.42.

Maybe the answer would be to just maintain the alkalinity at 90 by addiing baking soda, which would give -0.22 on the "Pool Calculator" and -0.25 on "Poolequations", and a Carbonate Alkalinity (ppm CaCO3) of around 79, still better than 98.8. If nobody else replies this what I think I will do.

My main question though is if I do not have to feed the alkalinity at 60 where it stays naturally, is 600 ppm of CH too much, and if so why, as the CSI is still negative. This would require less maintenance on my part.

Aloha.
 
Jason,

Of course you are right but as I understand it carbonate alkalkinity is better when it is lower in ppm. As the pool naturally settles at AlK 60, and if I can have my CH at 600 it would require less work on my part to maintain it and the acid would not be used up as quickly, if I am understanding the nature of carbonate alkalinity correctly aas it affects outgassing.

I would like to up the borates but as that needs twice as much acid to correct the inbalance the acid feeder has a hard time keeping up. I have tried that before and I had to supplement manually. Raising the CH to 600 and keeping the AlK at 60 would require less work and the acid feeder will be able to keep up. Next time I replace the acid feed motor I will go for a bigger one so that I can add borates to 50 ppm.

Thank you for answering my question, I know it drives you all a little crazy sometimes but I hope my explanation, hopefully correct, answers why I asked it.

I think I am done answering questions for quite a while.

Aloha.
 
As Jason says, for the CSI either the proposed low TA and higher CH or the current TA and CH are fine. It is not true that carbonate alkalinity is better when it is lower in ppm. It completely depends on the specific situation. If your pH were stable, then there would be no need to lower the carbonate alkalinity. However, in your situation, your pH tends to rise over time (so you have acid added to keep the pH down) so having a lower carbonate alkalinity may help by reducing the carbon dioxide outgassing.

I would try this: lower the TA to 70 or 60 where the water settles naturally (as you said) and see if the amount of acid that is added to the pool to control pH is reduced. If it is, then you are on the right track and can add the borates to provide more pH buffering (more of a safety factor since your TA is lower -- will help prevent pH swings if your acid controller gets too aggressive) and add calcium chloride to increase the CH level so that the CSI gets closer to zero.

Having the CSI be more negative for a short time while you experiment with the lower TA will not be a problem. It will let you see if that is worth doing.
 
Chem Geek,

Very helpful reply. Presently I have the pH down at 7.2 to do an in-pool acid wash, with an Alk of 90, CH 350, CYA 30, Borates 10, and the pH for some strange reason the water is much less demanding of acid than it was at 7.4 a few days ago, so once I get down to an Alk of 60, it was 130 over a week ago, due to adding lots of liquid chlorine I think, and I'm done with the in-pool acid wash I will report back. Plan on running it at a pH of 7.3 as this seems to be my magic number to stop iron deposits, thought it was 7.4 but faint traces appear, maybe even at 7.2, will rebalance at 7.3 first, then if no good go for 7.2.

Thank you for the crystal clear reply.
 
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