Thanks for replying- sorry I'm late in getting back to post results. I think what happened to me this time is that since my water tested 0 iron, I went ahead and shocked it right away instead of slowly bringing up my chlorine level. Unfortunately, I don't know for sure. You wrote that maybe I didn't use enough pool magnet; made me think; possibly I should have used the recommended amount of pool magnet for my whole pool, instead of just for the amount I filled, like the bottle said. It's totally a guessing game.

I went ahead and added more pool magnet, and this morning my pool's crystal sparkling clear! Looks gorgeous. Since I know I pulled that gunk out I backwashed and it came out a yucky brown color. I think it's safe to say that iron was the culprit. Good to go now. Thanks again for your input- you were right on the money.

I only use polyquat 60 algaecide .