I stopped by a friend's house to help him with his pool tonight. The pool is a vinyl IG with a deep end, 24" sand filter, and Hayward 400k heater. He claims it is about 30,000 gallons. The pool is crystal clear. He was concerned about the TA test going from green to light gold (instead of red). Here is what I found:
pH: < 6.8
CYA: > 120
The first time I checked the FC, I used the 25ml mark and gave up after 120 drops! The color would never totally clear, just go to a light pink. The second time I used the 10ml line and got a distinct transition to clear after 47 drops. I was surprised that adding the 5 drops of R-0003 showed CC. It took two more drops to clear it again. I find it hard to believe that there can be CC with that FC level, even with the CYA as high as it is. Is it possible that the low pH is messing with that part of the chlorine test?
Realizing that we needed to get a handle on the pH first, I used a base demand test to see how far down it was. After adding 30 drops of base demand to the pH color comparator and seeing no change (other than a lightening), I knew we were in trouble.
To attempt to bring the pH up, I added three 8oz whipped cream containers full of pH up (soda ash). I checked it two hours later and could discern no change. I then added about half a pail (guessing 15 - 20 lbs.). I will check it tomorrow morning and see if it moved. I realize that a partial drain and refil is needed because of the CYA level, but I'm really concerned about the heater with this extremly low pH.
FWIW, they appear to have gotten in this situation by using tri-chlor tabs in an inline feeder set on 7 (out of 10). The friend is under instructions to check the TA each day, and adjust accordingly. He has never been told to check the CL, just keep the feeder full. I have turned off the feeder.
Questions I have:
1.) I realize that low pH can affect the chlorine test. Does it affect both the FC and CC, or just one of them?
2.) The low pH seems to make the TA test go from green to gold. Even though its gold instead of red, is the value still accurate?
3.) Does low pH affect the CH or CYA test accuracy?
4.) Since the TA is related to the pH, as I raise the pH, I'm guessing the TA will rise as well. Would it be better to aerate to bring the pH up instead of adding pH Up, washing soda, or borax? I'm thinking this might keep the TA where it is now (which appears to be OK) while still allowing the pH to rise.
5.) With a CYA this high, at what level should the FC be considered unsafe to swim in?
I noticed that the solar cover is falling apart. It has the small triangle shaped "bubbles", and the bottoms of all of them are falling off and floating on the surface of the pool. I'm wondering if the low pH has destroyed them, of this is normal old age. I also noticed after leaving that my hands were very dry. I think this must be a function of the acidity of the water....
Sorry this is so long. Thanks for your advice.