picked up the fluval edge filter sponge. The way I have my rocks setup, I don't think it will be too visible.
I may give the sponge a haircut just to make it sleeker. Probably not necessary, but why not? got it for a $1.
still waiting on the nano diffuser. gonna give my current diffuser a trim too.
this is what I have been using:
and it really puts out a fine fine mist of bubbles. dirt cheap too