Background: 22,500 gallon fresh water inground gunite pool with pebble/plaster finish, Pentair WhisperFlo pump with 1.5 HP motor, Pentair vertical grid FNSP60 D. E. filter, Nature2 G sanitizer, Pentair 320 inline chlorine feeder, and AquaCal AeroTemp heat pump all located 30 miles north of Boston
This pool is 4 years old. I use the hockey puck size trichlor tablets. I try to maintain the free chlorine level at 1 to 1.5 ppm. Since we do have a mineral sanitizer I tried keeping the chlorine at 0.5 to 1.0 but felt I just didnít have enough margin during hot spells so this year Iíve been keeping the chlorine level a little higher to prevent algae blooms. I test regularly with a Taylor DPD K-2005 test kit.
I notice that the total alkalinity level is always dropping (I try to maintain 100 - 120 ppm). I did some internet searching and found that trichloro-s-triazinetrione lowers alkalinity. So I add sodium bicarbonate to compensate. Based on some additional internet searching I see that sodium bicarbonate has a pH of 8.4 so it raises pH. As the pH goes up I add sodium bisulfate to keep it at 7.4 - 7.6. I swear I end up spending more on balance chemicals than on chlorine tabs. Iím sure by weight I add more sodium bicarbonate than trichlor.
Is this really the way the cycle goes? Add trichlor. Trichlor lowers TA. Add sodium bicarb to raise TA. Sodium bicarb raises pH. Add sodium bisulfate to lower pH. This just doesnít seem right. Itís hard to believe after a few hundred years of pool chemistry this is the best chemical regimen for residential pools.
If this really is the state of modern pool chemistry, Iíd like to determine how much sodium bicarb I need to add to keep things balanced. In other words, if I add 1 pound of trichlor, how much sodium bicarbonate will I need to add? And if I add that much sodium bicarb, how much sodium bisulfate will I need? If I must constantly be adding sodium bicarbonate and sodium bisulfate Iíd like to work out a schedule whereby I just add the proper amounts every week or two.
I should mention that the pool water is crystal clear and has been all this season.
I also did some research on the pH of our rainfall. During summer most of our rain comes from the west, including the fossil fuel power plant rich Ohio valley. That rain is quite acidic (pH values of high 4ís to mid 5ís). So I would expect the pH to drift lower due to rain fall. But I never, ever, ever have to add pH plus chemicals. If we do happen to get a summer Noríeaster (not common) then the pH is closer to neutral but still acidic. So the vast majority of our rainfall while the pool is open is fairly acidic.