I think that's especially true of fissidens! I have some on a few smaller rocks along the sand. Most of it looks ok, but I had a couple where it mostly turned brown. I figured it was my glue job, although I tried to be sparing with it. Even the really 'dead' looking couple of rocks are coming back though! I have to laugh, I was worried about the Cyperus when I planted this tank, and almost didn't put any moss in the tank at all, for fear it would take over! Like, seriously, who struggles to grow moss? Well...me apparently