Luigi,

What is your TA level and your CYA level? A low TA (adjusted for CYA) could help explain your lack of pH rise. Either that or your SWG has somehow figured out how to output hydrogen gas bubbles without pulling out the carbon dioxide from your water!

You've probably got a fair amount of Borates in your pool. Two boxes of 20 Mule Team Borax (each is 72 ounces) would give you about 17 ppm Borates (measured as Boron) in your 10,000 gallon pool. That might be enough to act as an algaecide and that helps to cut down the amount of chlorine that gets used up fighting algae. So your lower cell output level means less hydrogen bubbles so less pH rise, but it is unusual to see no rise at all unless your TA is low.

Just to make sure, are you adding any chemicals to your pool on a regular basis such as non-chlorine shock or anything like that?

Richard