Just wanted to say thank you for this wonderful site and all of the great contributions. I was in a panic two weeks ago with our family party coming up next weekend as the pool was still extremely cloudy and was consuming chlorine like there was no tomorrow. The folks at my friendly local pool store were not much help, they'd test my water and say everything looked great. I'd mention the cloudiness and they said to just throw a couple of bags of shock in it...which i did multiple times.
Anyhow, I found this site, learned a bit and ordered a TF100 (which got to me super fast). I had been using a simple hth Cl/ph tester as well as ClearPool Expert strips. It turns out that the strips had led me astray a bit on the CYA level, they were showing a reading of 0-50. Luckily I didn't add any CYA as the TF100 gave me a reading of ~80 once I tested with that. I didn't have time to drain/refill the part of the pool to fix my CYA issue so I forged ahead with SLAM against the advice of the Chlorine/CYA chart. Using some Home Depot germicidal bleach (8.25%) I've been able to get things under control in about 3 days and now have a clear pool. Now we're just waiting for the FC level to drift back down which I'm hoping will happen in the bright sunshine forecast for all week.
I've seen it mentioned on here that people aren't sure how they got their high CYA levels but I'm pretty sure I know how I got mine. I always bought the Spring and Winter "kits" from my pool store which contain a bag of shock, a bottle of algecide and a bottle of conditioner/stabilizer. The kits are designed for pools up to 10000 gallons, quite a bit more than my 18' round, but they always told me to just dump everything in in order. My lack of any chlorine coupled with a late opening and green algae in the pool seems like it was a recipe for disaster when I added just a couple bags of shock and that whole bottle of conditioner.
Anyhow, thanks to TFP, the pool calculator, my TF100 and a bit of persistence things are looking up and I can't wait to get in the water. I plan to start following the TFP maintenance style, using regular items that I can buy less expensively than the pool store branded ones.