What is this black stuff growing??

[bkreitler]

So, the tank is almost 1 year old. Parameters are all good. Fish and coral seem healthy and growing, but I cannot seem to keep the sand bed clean - I actually don't clean it and was relying on a top notch clean up crew.... BUT, now this black sea grass looking stuff is growing. It is only growing on this side of the 310 gallon tank and seems to also be growing a bit on the rocks -- same area. It sort of reminds me of scuba diving in the ocean, but not sure I want this is my display tank. I assume it should go before it keeps spreading, but how? Manually taking it out?? I thought that it would be a nice hiding place for small fish and for pods. Any feedback?? Thanks!!

 

[attiland]

Probably algae some sort and just the blue lighting makes it look black but it is really green