I have taiwan moss and don't think it should have turned brown. It's really pretty hardy stuff. I'm wonderng if you kept it moist while you tied it down? That's the only thing I can think of that would have made it turn brown. It will not come back. I sit clumps of it in tap water at room temperature by my kitchen sink with no dechlor for weeks on end and it stays as green and nice as can be. I use excel in my tanks from time to time as well...without issue for the taiwan moss.