Have been using the Pondmaster Ultra Violet Water Clarifier in my pond for about five years, with good results. Decided to replace the entire unit instead of just the bulb this time. This is much better than using chemicals to control the algae.

I am well into year 2 of my new pond, I have a 15,000 gal. Koi pond and utilize 4 of the 40 watt units. My pond water has gone from green to pretty clear.I had a problem within weeks of installation, with one of the 4 units. I also was ready to give a poor rating on this product for bad customer service ..... but after several e-mails to Susan(SusanM@DannerMfg.com), she was able to rectify my problem with a defective ballast and is sending me a new one, along with a new quartz sleeve and a new bulb. (would have been easy if I had only had kept my reciept - word to the wise - Keep your reciept).I would recommend this product again - Patience please if you have problems with your unit. Susan just needed proof of purchase and date bought to allow her to make everything right (so it falls within the one year warranty). Business is business and I purchased it knowing it was a one year warranty. If there is a defect, I am confident the company will make good.** However, I would like to see a modification to allow cleaning of the glass sleeve to be a bit easier.PS - This spring I added more 40 watt units to my large Savio skimmer/filters. This seems to be the final touch my water needed. Now I can easily see the small stones at the bottom of my 5 1/2 ft deep pond.* I strongly agree with the previous fellow, Clean your filters daily (2X a day if needed until your water clears up), your UV lights won't work properly if its full of dirty water. If you don't have bio-filters, GET ONE (or two), they make a big difference and complete the natural filtration/cleaning process (savio makes a nice one).