Purple stuff on rock

[manuel732]

Can anybody tell me what's this on the rock
I touch it and it's very soft

 

[ebushrow]

Looks like Cyanobacteria to me ... just verify that it gets smaller when the lights go out and that's the one

 

[manuel732]

Ok thanks I'll keep an eye on it

 

[saltyhog]

It looks like it has little raised places in it? ebushrow is probably right but sponge and early development of red bubble algae are other possibilities.

 

[saltyfilmfolks]

if it blow off its cyano. But if it doesn't and has little holes Id bet sponge. Id actually bet sponge.

 

[eatbreakfast]

Cyano will be slimy, sponges are soft. I say sponge.

 

[fishkeeper2]

I vote cyano. Blow some current at it and see if it comes off. If it does, it's cyano bacteria. Time to get some Chemiclean. If it's cyano it can cover your whole tank.