Is this possibly coralline

[Merdfrog]

This green algae has appeared in the last few days. My tank has been experiencing a two week diatom outbreak which is finally on the decline. My tank is about a month out of cycle. I tries scubbing this new green algae off and it won't com off like the diatoms or hair algae. Could this possibly be early stage coralline

 

[blaxsun]

Quite possibly.

 

[Fishy888]

A picture under whites would be better. That said it looks like regular green algae of some sort. It usually takes a minimum of six months for coralline to start growing in earnest. Your tank is is only a month past cycling.

Coralline will grow in circular patterns until they all merge. The circles will have white edges. Coralline needs stability. There’s very little stability in a new tank. My own system is about seven months old. I’m seeing coralline growing on shells and on some rocks but it’ll be another five or six months to really coat the back glass, rocks, wave maker, etc. That assumes that nothing happens to majorly destabilize the system.