Black algae

[Fishquest4]

I have a 75 gallon saltwater tank with 20 gallon sump for a year now i havethe fallowing livestock
4 crabs
3 hermit crabs
5 snails
Bursa trigger
Coral beauty
Tomato clown fish
2 three stripe damsels
2engineer gobys
1 firefish
1 yellow tang
1 catfish shark
1 starfish

I have black hair algae growing or at least its what it looks like

 

[Misled]

It's cyano. read this.

 

[Ron Reefman]

I agree that there is a small amount of cyanobacteria there, the pink/purple stuff. But I don't think that is what the OP is asking about. And I've never seen cyano look dark (almost black) or hairy like it is in the picture.

 

[Misled]

Cyano can be unicellular, as in the matting form, or filamentous, which is what I'm seeing in the pic. They can also merge into a combination of both. The color seen can also vary not only because of type, but tank lighting, shadowing from tank lights, thickness, and the composition of the cyano itself. The amount of blue pigment, (phycocyanin) and the amount of red, (phycoerythrin), within the cyano determines the color we see.

 

[Ron Reefman]

Cyano can be unicellular, as in the matting form, or filamentous, which is what I'm seeing in the pic. They can also merge into a combination of both. The color seen can also vary not only because of type, but tank lighting, shadowing from tank lights, thickness, and the composition of the cyano itself. The amount of blue pigment, (phycocyanin) and the amount of red, (phycoerythrin), within the cyano determines the color we see.

Interesting. I've never seen it that way, but I learn new things everyday.