HI everyone, has anyone had experience with the UV light system and problems with getting nitrates down? I have a 29 gallon tank that I have one of these units in, and I am not having any luck getting the nitrates down. Everything else is fine. I have done several partial water changes and even changed out the very old gravel. Is it possible that it is killing off too much of the good bacteria? I have 9 mollies a guppy and 3 tetras in there and a couple of moss balls for plants.