Ok I have never in 30 years with this tank had this issue. Started with a sever hair algae outbreak!!! For the last six months hair algae it dies I clean tank change 20% water changes every three weeks or so… hair looks like brown diatom everywhere but grows like hair??? I removed and cleaned the rock, red slime outbreaks twice treated it this is now the third time. I have snails, crabs, cucumber, urchin, fish all eating some but snails and crabs are dying off urchin gone. Cucumber hanging in there. Water is good nothing is high please any suggestions? 90 gal tank with LED lights