Hi, all. It's starting to warm up a bit where I live, so I removed my pool cover this last weekend only to discover a green algae nightmare (by the way, last year was perfectly clear) . I think I closed too early last fall.
So, I began the SLAM procedure. First checked CYA - was at 0 after the winter closure. Used a sock to add some and am now at 30. Checked and adjusted TA and also made sure my pH was around 7.2. All good.
So, I got a bunch of bleach and brought the FC level up to 12-13ppm. After 30 minutes I rechecked and was back to 0, so I added more to return to 12ish. All going so far according to what I've read here.
But, here is where things get a little strange, I think. I checked again at the next 30 minute mark and the FC level was basically unchanged, around 11.5. So, I set about brushing all surfaces and then rechecked again at the 1 hour mark - barely lower, but the pool is still very, very green. To make a long story short, I have been checking my FC level (using FAS-DPD) every couple of hours and (easily) maintaining shock level, but the FC level is dropping super slowly, while tons of green remains. Overnight it only dropped by 3 ppm or so.
Is this normal? I had imagined from reading the sticky that the FC level would be dropping quite quickly while there was still a lot of green, and would only level off a bit once the green had turned to cloudy. Is this incorrect, or is there something strange going on in my situation? I'm not complaining, mind you - nice to not be burning through tons of bleach. But, I'm worried that something is not right, and the chlorine is not doing its job for some reason.