Welcome to the PoolForum!

Injecting CO2 into the water will lower the pH with no change in TA, but if the cause of pH rise is due to carbon dioxide outgassing the far better way to handle that is to substantially lower the TA level in the pool since that is the primary source of this rising pH. These systems aren't cheap, but you could price them out.

SWG pools also rise in pH due to other factors that may include outgassing of undissolved chlorine gas. The only way to resolve this, other than using longer pipe runs between the SWG and pool and to point the returns downward (but that is worse for surface circulation), is to turn down the SWG on-time. That basically means you need to reduce the chlorine demand in the pool and there are two ways to do that. First, is to have a higher CYA level closer to 80 ppm, but have a corresponding FC level of at least 4 ppm (Ben's Best Guess CYA chart says 5 ppm FC minimum) since that will reduce the chlorine loss from the UV in sunlight (if you don't have a mostly opaque pool cover). Second, is to add 50 ppm Borates to the pool which are a mild algaecide as well as a pH buffer so can reduce chlorine demand from nascent algae growth.

There are many people with SWG pools that have significantly reduced the amount of acid they need to add -- some have even gotten to pH stability. They have lower TA, higher CYA, use 50 ppm Borates, and generally don't worry if the pH settles in at 7.7 instead of 7.5.

Richard