Black algae on live rock?

[reeferfoxx]

Just like the title says except its more dark brown than sheer black. I have something dark growing only where the light shines. It's soft and slippery as opposed to slimy? lol This dark matter has been growing very slowly since the rock was introduced about 9 months ago.

 

Let me know, thanks

[wow.such.chris]

I can't say for sure but it looks like some sort of short hair algae possibly. I've seen some that looks similar, it's really hard to pull off of rocks until it forms bigger masses. I would bet herbivores would eat it. Nutrient control is the name of the game as per usual.

[Sancho]

Looks more like Cyanobacteria to me.

[reeferfoxx]

Thanks for the replies!

 

It's really dense. It doesn't sluff off like I think cyano does? I've never experienced cyano in a reef tank like I have in freshwater. I always thought cyano sort of dissipates with contact. This for sure would take a wire brush to remove.

 

Nutrient control... hmm. I've been testing my water lately and the only issues Ive had were a spike in phosphates about a month ago and low nitrates. In the beginning I didn't pay much attention to nitrates. I was feeding sparingly and skimming heavily. I've pretty much always done this. Then I realized after losing my first Acro, I was starving the tank of nutrients. Starving calcium, had ph swings and low nutrients.

 

The phosphate spike came from the addition of reef roids food and possibly a frag rack. After purchasing a goniopora frag, I was told it needed to eat. I think my increase in food in general was too abrupt. Then I placed the frag rack in the tank and left it kind of high up near the light. There weren't any frags on it, but the production of algae went crazy quick. For the most part the tank doesn't produce much algae at all. So I increase the photoperiod from 6 hours to 7 hours. That seems to have produce a little more algae now for the snails. After a month now, everything is ok and snails are eating but the brownish black stuff is still there...

 

This brownish black matter has been slowly growing since this tank was first established. I was wondering If it didn't have something bad attached to it?

[wow.such.chris]

If it was cyano it wouldn't be stuck on there very firmly at all.The way you describe it, I highly doubt it is cyano. If you saw a spike of P, I would say that is the cause. There's nothing especially bad about the algae that you're encountering, other than that it may look undesirable. As for the frag rack, anything smooth plastic is an algae magnet.