I have a 30000 gal inground pool,
with painted (peeling) plaster finish.
My fc is 1.0 combined is .5 (most of the time combined is 0. I was not home for a couple of days so free had gone to 0.)
ph is at 8 right now.
TA is 80
CYA is 25 to 30
Hardness is 300.
Pool is sparkling clear, smells and feels good. I do have just a very little very dark green or black scum just at and above the water line.
temp has been in the 80s for a couple of months now.
air temp in the 80 and 90s.
I am using BBB chemicals.
I add 2 to three quarts of 12.5% bleach each day after testing. This keeps my free between 1 to 3 parts. My PH started floating up just in the last three weeks or so. It had been relatively stable for months requiring only an occasional lowering. Now I have to add a quart every 4 to 6 days sometimes 2 quarts to get it back into range 7.5 to 7.8. What could be causing this? Possibly this black scum or ??