don't under estimate water flow under rocks. if i were to do mine again, i would have even better 'under rock' circulation. i grabbed one of my streams last night and 'created a storm' in my tank. the amount of detritus that had settled in my rocks was phenomenal to say the least. if you dont do this, consider bare bottom! (ugly, but less accumulation of crud) 'cooking' ya rocks (no, not with hot water!!!) maybe another consideration - timely but seems to work. too much time and effort imo.