I wouldn't say it's yellow and brittle, it just sort of sits there, doesn't grow, and eventually sort of disitegrates and disappears. Meanwhile, the unwanted hair algae grows lavishly on my live rock! I'm trying to figure out why the chaeto isn't doing a better job of controlling the phosphates that I believe are fueling the growth of the hair algae. I've read a bunch on this, and obviously it's a huge challenge to reefkeepers, but I'm not getting anywhere with the problem.