Kids hadn't used pool in a couple weeks because of cold temps. (Wisconsin). During this time I didn't look at the whole pool when I'd take readings- just pushed the cover back enough to get water samples. I didn't suspect anything was wrong because pH had been stable and FC only dipped low (around 3) when I hadn't checked levels for 3 days. Yesterday I pulled the cover off to find green/yellow/brown stuff sitting on the bottom of 50% of the pool on the side farthest from the filter. Colorful stuff felt gritty rather than slimy. FC was 3 and pH was 7.6, so I let the kids swim thinking it was pollen or some kind of sediment. All the "stuff" got completely stirred off the bottom and still hasn't settled yet. (It's been over 24 hours since being stirred up.) It left the water cloudy green and my pH went up to 7.8. Now I'm worried it's algae. But I haven't lost any chlorine in 29 hours! Could it be algae? I raised FC to shock level a couple hours ago just in case. I'm hoping my children don't become mutants now. Or that, if they do, they get stuck with the cool useful mutations that will give them superhero status in society.
1800 gallon, above ground, vinyl.