Algae

Get a sea hare from fish 4 you.  It works great.

Snails are cheaper. I'd see how well a few snails do before a spending $$ on a Sea Hare. Are you keeping the rock by itself? Low or no light and a couple snails could easily do the job.

Snails are usually very necessary to keep algae from getting out of control in a reef aquarium.

Red slime actually called cyanobacteria or cyano for short, is controlable by reducing feedings or other raw nutrients going into the tank. It's okay to let the fish go hungry for up to a week as the red slime goes away. With experience you will find how your feeding routine can effect cyano growth.

Edited by Mark Peterson