This month, I did about a 30% water drain from my pool. I figured that based on what I figure to be average and how far down I drained the pool. I let everything mix up a bit with the fresh water for several days and then I retested. My goal was to get the salt and cya back to what they should be. Since I didn't build the pool, I can't be certain of the volume. My experience over the past 4 years is that it is somewhere between 32-38000 gallons, based on the amount of chemicals, specifically acid, I have to add and also based on what I can measure in dimensions.
Before the drain, my CH was fairly high (pushing 600) and my salt was a little on the high side as well.
My salt and cya were, of course both very low. Salt was measured 3790 (my Zodiac Clearwater likes 4000 ppm, a little higher than other swg's) and my cya was 35, with a generous eye. It was probably closer to 25. I find this test to be very subjective. I even let the sample warm up to room temperature inside of my house for several hours before testing.
So I tackled salt first, since the pool is still cold and the chlorine demand can't be that high yet. I had 2 50 pound bags of salt laying around and the pool calculator told me to add at least that. I added it and retested a few times over the week. The salt was not raising noticeably! I figured at this point that I was underestimating the volume.
I then got some cya from my hardware store--Pace or HTH brand. I added 12 pounds, which was less than Pool Calculator's recommendations with conservative settings of 32000 and a starting cya of 35 (which I believed to actually be much lower since I could still see a shadow of a dot at 35).
This weekend I replenished my salt strips. The salt measured much LOWER than before (3200), which I figured was more accurate because the old strips were expired. I had my husband add ANOTHER 200 lbs of salt, slightly less than Pool Calculator's recommendation.
The next day (yesterday), I retested everything. I know it is less than a week since I added the cya, but I decided to measure that anyway.
Here are the numbers I got:
(I think the chlorine got used up because I started up my solar last week and there might have been some algae growing in there over the winter?)
TA 160 (my fill water is 210, so it went up as expected with the drain and refill)
CH 530 (not as low as I would have liked, but better than before)
What happened? How could the CYA and salt have risen like this? Should I wait a few more days and retest or tear apart the filter today and clean it thoroughly before any remaining CYA dissolves?
The salt I am not that worried about because it is well within range for the swg. The CYA I'd really prefer to have at around 80. I certainly don't want it any higher than 100! I did not bring the water up to room temp as before, but I thought that would give me a LOW cya reading? I did buy new CYA reagent, but this reading was using the old stuff that I had used for the original tests.
These things are now measuring as if my pool was a much lower volume than I know it to be as a minimum, not to mention the original 100 pound dosage of salt that barely made a dent in the salt reading....
What is going on here? Any ideas?