Saltwater swimming pools use chlorine generators to produce chlorine, which is released automatically in to the pool to maintain the recommended (free chlorine) FC levels.
A chlorine generator uses salt (Sodium Chloride) and water during the process known as electrolysis, where the two main byproducts are Chlorine and Sodium Hydroxide.
The byproduct Sodium Hydroxide has a very high pH level and will increase the pH level in your water.
It becomes much worse when your free chlorine production level is too high because for every chlorine produced, there is an equal measure of Sodium Hydroxide.
As such, the first sign that you have more sodium hydroxide (pH increaser) is when the free chlorine level (FCL) is too high in your pool water than the recommended level of 3ppm.
Another indicator that your pool is full of sodium hydroxide might be high Cyanuric acid (Cya) (chlorine stabilizer) levels, which in turn will make your chlorine generator produce more chlorine (and sodium hydroxide) to much the strength of the stabilizer and be effective in sanitizing the water.
Another common reason your pH level will rise unusually quickly is when the total alkalinity (TA) level is too high in your pool water whether saltwater or non-saltwater pool. As such, always make sure your TA level is between 80-120ppm for a saltwater pool.
In short, we have learned that pH rises uncontrollably in saltwater pools due to:-
1) Rise in TA and
2) High chlorine production level, which produces more high pH concentrated sodium hydroxide solution.
The only two ways to permanently control the pH level in a saltwater pool are to control chlorine production level and to lower TA level, and before you start working on your pool, you have to know what is causing the unusual rise in the pH.
Note that you can use a strong acid like muriatic acid to lower the pH level in your water, but if a high free chlorine production level is the cause, pH will reduce just for a short while and will shoot back up as more sodium hydroxide is produced during chlorine production.
How Do I Control Chlorine Production Level in My Saltwater Pool and Keep pH Under Control?
Chlorine production levels in saltwater pools can be controlled in the chlorine generator settings.
To slow down chlorine production, turn down the percentage settings in your saltwater chlorine generator to the lower settings.
If the FCL is too high, you can turn down your pump's run-time as well to lower it faster.
Also, make sure that your Cya levels are within the recommended range of 70 ppm to 80 ppm for a saltwater pool.
The most recommended way to lower your stabilizer level is by draining and refilling a portion of your pool water with fresh water, then balancing all pool chemicals starting with the pH and Chlorine in that order.
Once you keep the chlorine production level under control, trust me your pH level will be under control as well. For more visit how to fix free chlorine problems in a saltwater pool.
How Do I Control the Rising pH Level in My Saltwater Pool Caused by High TA Level?
When sure the pH rise is not caused by a high chlorine production level that releases more sodium hydroxide into the pool, or a high stabilizer level in your water, then your TA is the cause.
Borax is a more stable pH increaser and the pH level will be stable within the level you raise it at and will never increase unusually unless you add a pH increaser. You will also save on acid since the pH level will be stable for long while:)