I have a 5000 gallon pond with 18 fish (mostly koi) and about 50% plant coverage. It is in full sun all day in southern California. Without plants the visibility was only 6 inches. With plants and bio filter and so on I still could not get the visibility beyond 18 inches. I had tried chemical algae killers but with all the sun we get and the warm water they can't clear the pond and also the algae comes right back in a week or so. Also I did not want to become dependent on expensive chemicals (nor kill my fish!). When I installed the Pondmaster UV light I noticed small improvements in visibility within 24 hours. Within a week I could see down about 3 feet. It took just a bit over two weeks until I could see the bottom (at 5 feet). Since that time the clarity has improved further so I cannot only see the bottom but I can see it very clearly.

It cleaned up the pond and maintains it well. The only problem that I have with the design is that the socket gets corroded if you don't clean it before winter and keek it clear

So far, so good. I have not seen the bottom of my little pond for two years. After cleaning the pond and putting this light in, the pond has been clear. I hope this continues throughout the summer.

I was skeptical of all the UV hype but after two months of trying every natural method I could find I took the plunge into UV.This Pondmaster 2940 40 watt model seemed to have a good rating from users and more important it looked like it would physically fit where I needed it to go.My pond is not huge, but is in direct sunlight for most of the day. I've added numerous plants to help control the amount of sunlight getting in and the water continued to get greener.The pond is about 1200 gal. it's 2.5 ft deep at the deepest, about 18 feet by 4 feet, several shelves for shallow plants and a small extra shallow bog area. The filtration and pumping is handled with a 3 inch bottom drain feeding a 32 gal settling tank that is plumbed directly to the Sequence 4500 external pump. There is also a small pool type skimmer keeping the surface water clean that feeds into the pump line directly. That pump sends the water up the small incline to a 32 gal bottom feed Skippy style bio-filter full of mixed poly media. The water free flows out of the tank into a small rock filled creek to aid in aeration of the water. BTW the pump is restricted to a much lower flow than maximum rating.I was able to place the Pondmater 2940 in the settling tank and connect it directly to the outlet of the tank going into the Sequence pump. This was one of the most highly recommended places to put the UV so all that dead algae would be sent directly to the filter. The UV was positioned vertically and the ballast is above the normal high water line in the tank. My water was so green that the first glow ring on the UV was not visible in the tank and it is only about 3 inches in the water.After 2 days of UV treatment, my green water pond became the oddest gray water zombie death pond I have ever seen. It was the color of death. Algae death! There was so much dead algae I put a simple flow through trap in the stream bed to try and get all the flow thru from the filter. there was no way the biobugs were eating all this.I did a partial 15% water change on day 3 and another on on day 5. I also agitated the bio filter and pushed the gunk water out of the pond and watered the lawn with it. :-) On day 5 the gray vanished, the water was clear(er) but the bottom was still hazy. The clearing continued at an amazing pace and on day 8 my pond was completely and totally free of free floating algae and crystal clear. UV clarifier/sterilizer really work. I'm a convert. I'll never build a pond again without planning the UV into the process.Your results may vary from mine. I know this 40 watt UV unit is over sized for my pond capacity. Everything on this pond is over-sized. I can't comment on how durable the unit is except to say the construction is good. The fittings are solid and the isolation of the UV light seems good. Obviously the flow and dwell time in my setup is good. The pond has stayed crystal clear now for over a week and we just went through the summer solstice so the sunlight in my back yard is as strong as it gets right now.The unit is solid, easy to install, plenty of power for larger installations and it works!

great uv output. cool light that lets you know its on. this is large uv unit and works well for my 3000 gallon pond

We finally decided to spend the $ to get a UV light and so glad that we did. Within 7 to 10 days with it running 24/7 our pond was completely clear! It is incredible, we can even see the fish swimming through the roots of our pond plants. This is a great product and love the feature of the external lights on the device, that let you know that it is working. Fish are so healthy and happy that they can see each other! Lol

Well I followed the instructions and within seven days our pond is crystal clear.I don't think the fish are all to happy to be seen all the time but it looks great!One caution its obvious the way the bulb is sitting in the quarts sleeve if you knock it to hard you will either dislodge the bulb or possibly break it. Be carful. Also the three illuminating rings we distracting enough for me to rap them in extra liner material if you don't it looks like something from another world glowing a the bottom of your pond. LOLGreat product.

Great product , keeps the water clear very well . The only submersible uv I could find and very happy with it. !

IT SAVED MY KOI !!!!!!!!!!!! + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + ++ ++

This product works as advertised. I have had no floating algae since using the UV clarifier. I have had no problems with the light since I installed it 3 months ago. The glowing bands on the top and bottom of the light make it east to check that it is operating.

I have a 12,000 gallon pond, twice the recommended size for this product. I coupled it with a Laguna Max-Flo 2900 pump, slightly less than the recommended maximum 3000 GPM, lowered the amount of pea-soup water to about half and left them working. Did the job in two days. I filled up the rest of the pond with clear, fresh water. A couple of days later, the pond was even more clear! Although I am satisfied with this product, I would have appreciated additional information such as:1) The water inlet and outlets are 1 1/2 inches, serrated as to hook up to a hose. There are no connectors for it. Get them. This was the biggest hassle for me.2) The light and its casing come apart, not assembled. It is pretty easy and straightforward although there should be instructions about how tight to fasten it. I was afraid of putting lo low or too much pressure and damaging the product. I chose light pressure and it worked fine.3)It is recommended that you change the light AND its casing after 6 months of continued use. Had I known this, I would have included them in the original order.4) the screw-in connectors do not have to face each other but be left at different angles, making it easier to hook it up.5) This water clarifier measures about 30" in length.

I rarely write a review, but wanted to say a few words that might help anyone thinking about buying this product. The water in my pond looked like pea soup. I did partial water changes and cleaned the filter twice a day, nothing seemed to help. Finally I bought this, although I was kind of a skeptic. The first few days I didn't think it was doing anything, but as the days went by it got better and better. After a couple of weeks the water was crystal clear. Amazing!The clarifier does NOT come with attachments to connect it into the pump and into the filter. We took it to the hardware store to figure out what parts we needed to connect it all, so be prepared!!

Within one week my fish pond was clear. I can now see the bottom. The light runs continuosly and uses little electricity. I would recommend it to anyone looking for a fast fix to murky water.

So let me try to make this story short. I basicly got this UV sterilizer 3 1/2 to 4 years ago used from a friend of mine that owns a pet shop. The previous owner and I invested in the sterilizer for our saltwater aquariums. The unit was pretty new, I think it had been used for a year or less. Used the unit for my 90 gallon saltwater tank for approx 3 1/2 to 4 years with really no problems. I even moved a year ago and hooked the unit back up to my tank with no problems. Every once in a while i would have to tap on it alittle when I plugged it back in after doing a water change on my aquarium. 6-8 months ago I notice that I had small puddles of water around my aquarium on tile floor or stuff under my tank was wet( I have unit sitting ontop of my home made wet dry filter under my tank. Thought at first it was just water splashing from where it pours into wet dry filter. Negative,noticed one of the halos on unit was leaking alittle. At this time it was just a constant drip of water, which over months increased to a small squirt of water at times. Took care of that by placing something over leak where water would drip/stream down instead of squirting up and weting my tile floor. Have notice increase in water on my tile floor last couple weeks. Got off work one morning to find that the halo had started squirting so much water out of aquarium that the water level got low and my water pump could not ciculate water in aquarium. This caused my saltwater fish to have a lack of oxygen over who know how many hours!! Almost lost several fish, ended up that only my lunar wrasse died from inccident!! I am upset, but I did get 3 1/2-4 good years with this sterilizer!! So does anyone know how to fix the halos to keep them from leaking or should I just buy a new sterilizer??? Halos are not cracked and it is just 1 halo that needs repairing. Any ideas?????? Over all a good product.

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.

This product works just as advertised. My water was clear within a week and has remained clear after installing it 3 weeks ago. Also, it was easy to install and it is money will spent.

Out of all the pond UV lights to control algae in ponds I think Pondmaster is by far the best ! I have a large pond so I chose the 40 watt unit. Most of all the submersible unit is great it is vitually invisible!~ We also build ponds for a living and this is the unit I put in my new pond constuctions!

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).

I have medium sized decorative pond that gets harsh western sun from about noon until sunset. Ironically, the algae got worse in winter. Visibility in the pond was down to about 1 inch. It was positively disgusting and it stank.2 week after putting the Pondmaster UV filter into the pond, the water was clear as crystal.However, as the manufacturer indicates, "filter" isn't the proper terminology. It's a sterilizer. It doesn't eliminate the need for a normal bio filter. This kills the algae and other parasites so the bio filter can remove them from the water. If you have a particularly green pond (as I did) clear the filter pads weekly until you've regained control over the algae.Again, note that the UV system addresses free algae - not the string algae that grows on the sides. It's basic logic - if the algae is stuck to the side, then it can't pass through the steriliser to be killed.Change your filter pads regularly until you've gotten past the 2-3 week period when you're waiting for the pea soup to vanish. All that dead algae needs to be removed. Make sure you get any old leaves out too - that will speed things up.If you don't see results, make sure you have the right wattage, and also adjust the pump to ensure the water isn't moving to fast. Algae cells need about 1-2 full seconds exposure to the lamp to break the cell membrane and kill them.Bottom line - it does PRECISELY what it says.