new brown algae, established scrubbed tank

[nathan32387]

I just recently started getting a thick brown algae on certain spots of the sand bed, they appear mid day and are gone the next morning, currently running a HOG.5 and skimmer and recently added a HOG3 when I realized my nitrates were over 80, both scrubbers are growing super thick green hair algae and nitrates have dropped to 5 as of this morning, the brown algae only started appearing recently and has small bubbles attached to it, any ideas on what it might be? and how to get rid of it?

[Pny]

Looks like dinoflagellates...

[SantaMonica]

Welcome.

I think it's probably cyano. Cyano will often be the last nuisance algae to appear, after other nuisance algae have gone. This is because the cyano could not compete to get the space and/or nutrients it needed before, but now with the other algae gone, it can. Plus, cyano usually does what you said: appear during the day, and go away overnight.

As your nutrients drop farther, it should go away. You can speed this up by making more water flow along the sand; this keeps food particles from settling there (food particles give carbon to the cyano). Also any type of sand-stirring CUC, like a diamond back goby, will keep the sand really white.