Purple Growth

tyrfing

Member
I'm posting this here even though my tank is 4 years old. I figure I could probably get some good answers because I have a feeling this is a basic thing.
My 75 gallon tank has 80 lbs of live rock and a DSB. Only four fish currently, a Chromis, 2 clowns and a Royal Beauty Angel. Two cleaner shrimp, various red and blue hermits, around 15 snails, bunch of sea fans, some HUGE leather coral that won't quit growing and a couple of stars.
Anyhoo..
About a month ago I started getting this deep velvet growth on the live rock. It's spongy, about 5 mm thick. I can pull it off with my fingers and it will come off in sheets. But, grows right back. I vacuum it off during weekly H20 changes, but four days later, it's back.
Any clues as to what's going on and what I can do to get rid of this stuff?
 
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