high ph and good alkalinity in salt pools

Problems relating to pH and total alkalinity.
Increase ph, increase TA. Reduce pH, reduce TA.
pH chemistry advice and techniques for the pool.

high ph and good alkalinity in salt pools

Postby bill » Mon 08 Sep, 2008 00:22

Having troubles lowering the PH in my salt system pools even though my TA is at acceptable levels. What can I do to combat this problem? I have added muriatic acid, but it only seems to lower the alkalinity and not the PH

chem geek
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high ph and good alkalinity in salt pools

Postby chem geek » Mon 08 Sep, 2008 01:53

SWG pools tend to rise in pH due to a combination of factors including greater aeration of the water and some outgassing of chlorine gas that doesn't get completely dissolved. There are several ways to solve this and can be used in combination for greatest effect.

First, is to lower the Total Alkalinity (TA) since part of the reason for the pH rise is the outgassing of carbon dioxide from the pool (pools are intentionally over-carbonated). In an SWG pool with 60-80 ppm CYA, the TA can be lowered to around 80 ppm. You can go even lower if you raise the Calcium Hardness (CH) level or target a higher pH level (say, 7.7) so as to keep the saturation index closer to zero. You can use The Pool Calculator to calculate the saturation index -- don't forget to include the salt level. You lower the TA by following the procedure outlined in this post which is a combination of acid addition with aeration at low pH (or if you just run the SWG and add acid regularly, the TA will drop over time unless there is lots of evaporation and the fill water has high TA, though this takes longer compared to the procedure at low pH with extra aeration).

Second, is to target a higher pH and not try and fight to get to 7.5 or below. The combination of higher TA with lower pH results in much faster carbon dioxide outgassing which makes the pH rise faster.

Third, is to use a pool cover if possible. That virtually eliminates the outgassing as well as lowering the loss of chlorine due to sunlight, letting one lower the SWG on-time.

Fourth, is to make sure the Cyanuric Acid (CYA) level is 60-80 ppm, preferably 70-80 ppm. This cuts down the loss of chlorine due to sunlight which lets you lower the SWG on-time. The Free Chlorine (FC) level should not be below 5% of the CYA level (so 4 ppm FC if the CYA is 80 ppm).

Fourth, is to add 50 ppm Borates to the pool. This can be done with a combination of 20 Mule Team Borax and Muriatic Acid added alternately or more expensively (but more conveniently) using pH balanced Proteam Supreme Plus. The Borates are an additional pH buffer, but also are an algaecide that can lower chlorine consumption. Lower chlorine consumption lets you turn down the SWG which lowers the rate of pH rise.

Fifth, make sure the returns are not turned upward, but are pointed slightly downward or at least straight across. You want the chlorine gas output from the SWG to spend as much time in the water as possible so that it fully dissolves and you also want to minimize the amount of aeration and surface disruption (unless you are doing the "lowering the TA" procedure).


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