Hello forum. First, let me say THANK YOU to all of you for this awesome repository of knowledge. In the few days I've been reading posts as well as perusing the Pool School, I have learned more than the cumulative 3 years I've been maintaining my pool. Also, local pool stores are frustratingly inadequate for those of us wanting to learn, not just react. So again, thanks.
I'll try to be concise by saying that I have a CYA problem. I didn't know I had this problem until my local pool store finally told me that it was off the charts. Never mind the years before that during which they and 2 other shops never said a thing. Nor did they see anything wrong with endlessly feeding trichlor tabs into my 10Kgal pool without ever replacing water (I have a cartridge filter and never have occasion to remove water).
I couldn't keep chlorine in it and they took a guess at my CYA level being 300 (!!). So I drained the water, twice, and shocked and adjusted. Things were OK. That was a couple months ago. Now again this summer I'd been getting algae blooms at what I consider normal chlorine levels (4-5ppm) and even superchlorinating to 10 wasn't fixing algae or cloudiness. I'd get answers like "put a whole jug in and wait 24hours" etc. Maybe that was right, maybe not. But I finally searched and wound up here. The key of course is my CYA level and the fact that with 100ppm of CYA, 10ppm of chlorine doesn't do squat
So I drained half again, for the third time. They'd told me my CYA was 100 and thus replacing half the water would get me to 50 and using the chart, I began my SLAM with a shock to 20ppm. First night I lost 3ppm so I kept it at 20 the next day. Second night I lost <1ppm so I'm happy. I'm letting the chlorine level come down and the pool looks much better than it has in months. It's starting to sparkle again.
Today my full test kit arrived and I decided to test the CYA levels for the first time. First run, I was nowhere near the 100 line. I diluted 2x with distilled water and ran the test again. ~60, giving me a final number of around 120. Now I know the CYA test can be subjective but this means I'm still off the charts.
How is this even possible? if I'm at 100+ now, that would have put me near 500 before I started all this, clearly leaving me in a place where my pool was completely unmaintainable. Granted, I'd been popping powdered shock and chlorine tabs like they were going out of style...
I guess my only choice here is to replace half the water again, and maybe even again? How subjective is the CYA test? Any tips on optimizing it?