U/V sterilizers are great when used properly. I think that UV's are marketed to the public wrong though. In order to be efficient, even if its going on a 20 gallon tank, a sterilizer needs to be 25 watt. There are so many variables to consider. What is it that you are trying to kill? Certain bacteria/spores need longer contact time. Also, don't put your sterilizer in line with your filter. It needs to be on its own pump. If you can find this book AQUATIC SYSTEMS ENGINEERING I would by it. It explains how every piece of equipment on an aquarium works and gives you formulas and calculations to make that equipment work at its peak efficiency. The book is out of print and very hard to find. Amazon has one for $120 and its original cost was 29.99. Send me your tank specs and I'll try to figure out what pump you need to use. Generally you will want a low flow rate, but with a nine watt sterilizer it will need to be on 24/7 to effectively reduce bacteria and algae in the water. with a 25w you can sterilize 99.99% of the water twice a day and run it for maybe 2 cycles of 5 hours per day (depending on tank size).
