Close to but not quite. Almost every salt pool we service (467) needs a ph adjustment every week of a small amount. We had a guy named Jim from stain drop (ex jacks) speak to my company about this and they said the number one problem of salt water pool finishes is scaling and a direct result is high ph for prolonged periods. Coincidence? Not at all. I think the real issue is the home owners or even pool guys run the SWG at a much higher output than necessary and that is a direct result. So to say that there is no ph change with a salt water pool is simply not accurate. Of course other factors here too as we know such as alkaline levels etc. I’ve heard the uv theory yes but there is to much proof otherwise.
I'd happily argue with anyone about this topic and I'd win because the chemistry is settled. Please see this post in our Pool Water Chemistry thread written long ago by an expert in chemistry -
Pool Water Chemistry
(Unfortunately, due to our forum software update, the BBcodes for superscript and subscript are not working so it makes reading the chemical equations on that page a bit difficult)
If you read through the chemistry of chlorine additions you will see that an SWG has
net neutral pH. When chlorine is generated inside the cell, the pH will increase a bit from the formation of hydroxyl ions (OH-). However, all chlorine sanitation and oxidation reactions are acidic (they generate a H+) and so the net effect is no change in pH.
The primary driver of pH rise in ALL pools is the water we we use and the outgassing of CO2. All surface waters and most well waters have carbonate alkalinity in them and it can be quite high. The TA of my fill water is 100-120ppm. When a pool has high TA (anything over 80ppm) and the fill water has high, there is a constant upward drift in pH caused by the outgassing of CO2. You can think of pool water like a can of soda, the liquid inside the soda can will have low pH to start but, once you pop the top and let the bubbles out, the outgassing of CO2 raises pH. Pool water acts in exactly the same way - TA measures, in part, the carbonate alkalinity of the water (how much dissolved CO2 is in it). As the CO2 outgasses from the pool water, the pH rises through a series of equilibrium reactions. This is a well known phenomenon and can be found easily with a search of Wikipedia.
Pool owners experience pH rise when the switch to SWG's NOT because of the SWG but mainly because they were previously using an acidic form of chlorine (dichlor powder and/or trichlor pucks). The acid released from those chlorine sources would slowly reduce TA over time and help suppress the natural pH rise of the water. Then, when the switch is made to net-neutral pH sources of chlorine (SWG's or liquid chlorine), there's a sudden rise in pH because there is no longer anything acidic being added to the pool. As the old adage goes, correlation does not equal causation!
It is simple to prove this and I have done it before - simply put a bubble cover on the pool and stop the outgassing of CO2. When I have a cover on my pool, my pH remains totally stable and barely changes for weeks on end. Without a cover, it will start to rise. And it doesn't matter if my SWG is on or not.
The fix here is simple - lower your TA. I keep my TA between 60-80ppm. If I do that, along with using borates as a high pH buffer, I can easily go 10-14 days without having to add any acid to my pool. Unfortunately, the Industry people will tell you that a TA below 80ppm is BAD for your pool and that is simply wrong too. So the Industry likes to ignore the detailed chemistry only to cause more problems and further lack of understanding.