Over the last couple of days I have notices that a couple of my rocks are starting to turn this yellowish brown color. Along with that, it is falling off the rock and covering the sand. Is this normal. My tank is fairly new. I dont really have anything in it to keep it clean, as far as a cleaner crew goes One turbo snail and one little hermit crab. And it just settles into the sand, so my filter isnt picking it up. Am I ok or should I scoop it out