I have been told that the brown dusty covering on my rocks, sand, coral, and anything else horizontal is diatoms. "No problem," I'm told, "cut down on feeding' and "it may be your water." This tank has been set up for over 10 years. I had the problem once before (slightly, compared to this) - when I didn't have coral (fish, urchins, starfish only) and it did eventually go away. It's been@ 5 months now and I've been using a turkey baster to blow it off of everything every few days. Then in 2 days it's back. It looks awful, doesn't seem to bother most of the inhabitants but I'm worried about the star polyps. The stuff really sticks to them and I do seem to see that it's not as bushy as before. It rinses away when I squirt them with the baster but I'm afraid if I go out of town it will be dead when I return (I don't trust my fish feeder to do anything but feed). Any ideas? I can't use RO water (never have) because I have to drive 1.5 hrs (there & back) to get it. I also think that I would have seen it get bad before now if that (the water) was the problem. BUT..... I need some opinions... Thanks!