
The "lettuce" is the algae that formed on the top glass in the tank (above the water), I'm not fully sure how to utilize it best (it is fairly thick and looks tasty), for now I put a couple of pieces under the stones...maybe it can grow under water too. After a fight, the cteno you see below owns this place:

I __think__ he actually ate some of the stuff, the green on the Gastro itself are the algae threads caught in the fins:

There are a few losers sitting around and waiting for him to leave....