Newby with problems, times 2.

I have an older pool with a Nautilus FNS DE filter and a Pac-Fab 1hp pump. Just started the Spring opening and my water is dark green pond status. I took the filter apart and cleaned the grids and added DE. Now large amounts of DE are circulating back in the pool. The grids are nearly new by the way, installed at the end of last season but all last year my water was a little cloudy so somehow DE must have been blowing back in.

I pulled it all apart and reset the grids as tight as I can get them and DE still goes into the pool. I decided to let that rest for the day until I could figure out what to do-any ideas? I don't think I have a cracked grid or bad manifold or connection.

Also, since we have a long haired dog that gets in the pool a lot I thought it would be a good time to check the impeller for debris. I pulled the pump apart and to my surprise, it was relatively clean. I did notice that the o-ring that surrounds the impeller housing appears to be stretched so that there is slack in it with no tight seal. I re-installed the pump motor and fired it up in circulation mode and it pumped a little but most cavitated and was louder than normal-sounded like it was running dry.

Would the small o-ring being slack cause it not to create proper suction? Any good sources for replacement rubber in the Atlanta area?

Thanks.

JB

BTW-not a total newby to pools, just new to the forum.