Is this a blue-green alga? Anybody know the species?

[Tiny Ocean]

This stuff grows slowly on the ceramic filter media balls that I keep in my culture jar (a gallon of brackish water specifically for growing heavy amounts of bacteria, algae, and biofilm in case I need to add nutrients or hastily inoculate new water). It has been going for over a year. I have assumed this stuff was a blue-green alga species but now I am not so sure. It smells faintly earthy and maybe a bit bitter, not foul, and it isn't (yet?) a slime. It forms a puffy velvety nub on several of the ceramic balls. It is a deep green rather than yellowish-green color and I actually like it. If it would cover the media balls it would look cool, sorta like moss balls. I'm concerned though because the opae ula don't seem to eat it. I don't want it suddenly exploding and fouling my culture jar , or introducing a harmful organism into an opae ula tank, or putting out toxins.

[Tiny Ocean]

another view