Hey folks ... I'm about to do a water change and noticed a nice layer of brown dusty stuff 1/8th inch thick on the bottom of my wet-dry under the bio balls. I also see some little critters (amphipods?) runnin around in it. I'm about to drain my wet-dry and clean all that muck out of there and It'll be hard to leave the critters behind. Am I about to take good stuff out of my tank?