>>Out of curiosity, I'd like to know if there is any driftwood in this tank. >I have two pieces in this tank. If all else fails, try removing the driftwood. If you have any other "dead stuff" in the tank, that may or may not help. "Dead stuff" includes peat or any other organic material in the substrate or filter system. I'm not saying this is the cause, just trying to test a theory. Tom