Acans receding - looking for suggestions on possible causes

[Borderjumper]

I've had this happen a time or two with acans. mostly colony's on rock. Cutting off the dead parts I've found the rock to have very foul smelling black holes, and in some cases a very small bright red worm. The worm isn't any thicker than a piece of string and maybe an nice long. If I notice an acan even looking slightly off now I give it a soak with a tiny bit of hydrogen peroxide. It seems to perk them right up.