Thank you for all your help so far. You are right, I am posting on 2 forums. I posted them at the same time because I did not know which forum is better since I have not even been to a pool forum until I started having this problem.

I have a Hayward sand filter. I dont know how old it is, because we just moved in the house, but my guess is that it is about five years old. It appears to be in good shape, however I do have a concern about it; I notice trace amounts of sand in the "view glass" during backwashing and I notice that my polaris is picking up very small amounts of sand. This makes me wonder if I have a sand "leak" and if so, if that contributes to my problem. My piping is fixed to the filter so it looks like it would take some sawing to get the filter apart to look in.

I did add some algaecide to the pool a few weeks ago. It was the over the counter Aqua Chem stuff that you buy at Wal Mart. Can that do it?