A very interesting and good discussion on uv. I can learn a lot from this thread. I have been used a uv unit which I find it quite good. This uv was routinely used in fish farm which need to handle a huge bioload. The advantage was high power , small housing and no need to replace the bulb so frequently. The disadvantage was the need to have water inside the tube all the time and it must cut off the power supply if the water was stopped. The analoge between this uv and ordinary aquarium uv was just like metal halide vs flourescence tube. http://www.troptronic.de/TT_Frame_e.html Just my 2 cents!