CUTURHAIR I was having a similar issue as yours, mustard algae on the sides, shelfs, etc. My problem is now gone. I held chloring at 16-20PPM for 2 days, kept pump running and put in a quart of polyquat and brushed sides. Then I let the chlorine come back down. So far it has not returned and I am doing maintenance doses of polyquat.

Polyquat is usually used as preventative but it does seem to kill algae as well. I have large fountain with a pump that is always getting algae in it. Just for kicks I threw in some polyquat and it cleared up the algae and also made the water in the fountain incredibly clear, I was shocked how well it did.

good luck,
-- john