rising ph levels

[chem geek]

I use a cartridge filter and it's 3 years old, so I don't think my filter could be a contributor. I only use bleach, muriatic acid and baking soda. Nothing else. My swimmer load is very light this year, but I have not seen much differnce based on swimmer load either.

Well we have a mystery then. I'll double check my calculations since I could have made a mistake somewhere though I've used the same calculations elsewhere where they've been more consistent. Also, as has been pointed out in other threads (Saturation Index in The China Shop), the science can only go so far because the pool is not a closed system. Still, it would be nice to know the source of this base to cause pH to rise -- it must be annoying to have to add chemicals so frequently. Might be time to look at investing in a pool cover

[EDIT]I verified the calculations and don't see anything wrong with them. Because you haven't seen any change in the amount of acid you have to add when you were at a TA of 80 vs. a TA of 120 and because you don't see a drop in alkalinity over time, I think that rules out the outgassing of carbon dioxide as the source of the problem. So we are still left with what is adding base to your pool. Both you and "CToon" both have vinyl pools, I wonder if that has anything to do with the problem or if the low CH is a factor. Anyone else out there with a mysterious rising pH? Do you have plaster pools or vinyl pools and if vinyl pools, what's your CH?[END-EDIT]

Richard