I was using one for several months. The bulb would burn out about every 6 weeks to 2 months, and cost me $45 every time. Then I talked to Will at Premiere fish and reef at the January meeting and according to his research, on an average size tank, you would have to use several hundred watts of bulb to kill any unwanted parasites and it would have to be at a trickle flow. Most of the units on the market are only good for killing off free floating algae (green water). Since my water was clear, and I use a carbon reactor, I decided to stop using my UV. Didn't notice any change in anything in my tank or chemistry, and I still have to clean my glass every few days regardless of whether the UV was running or not.