Purple death :(

[bertoni]

That shouldn't cause much damage, most likely, but I'd leave the rock in the tank and siphon-clean it.

 

[rafa316]

Today I cleaned as much purple stuff from the sand of the tank, also cleaned the mechanical filtration of my fuval 405 tank. I took a sample of the stuff to the fish store today, they did a water test and it showed my phosphate was really high. I was trying to lower the levels by ussing a cheaper phosphate control medicine, but today I bought PhosBan and placed the medication straight into the filter, Hopefuly this will help.

 

[kuoka]

If it's red slime, I've had luck using chemi-clean. You should also cut back on the feedings like mentioned before and use RO/DI for top offs.

 

[jaymz101]

Cyano also likes low flow areas. Try directing a powerhead on it and reducing the amount of food you feed. Watch your fish when you feed and take that small pionch or whatever and dose it out over a few minutes. When the fish stop eating, stop feeding.

Be careful buying crabs to deal with the problem. Small crabs might eat the bacteria but when they get big (and they will), most crabs become opportunistic and can pick at corals and the occasional fish.