Not enough info...clear the water of WHAT, exactly? What prompted the purchase of the UV?

Is your water green? brown? cloudy? Do you have a bio filter? If so what kind? How many gallons? What's the ratio of water:plants? Do you have fish?

Lots of experienced ponders here who can steer you in the right direction but all of this info in important in diagnosing the problem.

happy ponding,
~digger

For green water a UV should clear water in 3-5 days imo. The change can seem sudden if you wake up in the morning and can see the pond bottom. What really happens is the algae is killed pretty fast, maybe 8 hours. But it takes some time for the green to decompose out of the cells leaving an almost translucent cell behind which are also smaller. Some clump and sink.

What UV do you have? 10-14 days bothers me. Clarifier is not a precise term, so sellers can get creative. Most manufacturers provide info on flow rates for both sterilizer and clarifier. I always use the sterilizer flow rate when comparing units, apples to apples. Taking 10-14 days could mean a very weak UV for the advertised flow rating. In a bright green pond single algae are that, single cells, easy to get a high UV dose. After a year many cells will have clumped together into what is called "colonies". They do this as protection from the sun's UV. It also gives them some protection from UV filters as it takes many more trips thru the filter. Add a bunch of other suspended particles, plus a weak UV, could be issues.

Diggery is right, not enough info to really know anything. A red flag to me is a pond that hasn't been clear in a year may appear green but be a combination of things. After cleaning different ponds for awhile you're able to tell a lot from just seeing the water.

Agree with the others. A UV needs to be properly sized to suit the pond with the proper flow from the pump. Too much flow sends the water past the bulb too fast to do any good. Too low of a flow can't keep up with the multiplying algae.

Also, you may need to check and make sure the bulb is working. DON'T LOOK DIRECTLY AT THE BULB. Its very bad for the eyes! Look at an angle into one of the hose openings. You should see a purple or bluish glow.

So the pond is around 4000 gals (actually 2 ponds w/ a stream connecting them). It has a bead filter appropriately sized. There's a water lily in each pond covering may 1/4 of the surface and misc. other plants as well. There are a few gold fish (maybe 3 or 4 less than 6" long - thank you Mr. Heron). Quite a few frogs so they probably contribute more to the bioload than the fish. Ponds are in full sun most of the day. Water is bright green with no noticable clumps of algae so I assume it's just a few bizillion of the single cell variety.

Can't recall what brand the UV is but it's 36 watts and was rated for this pond size. I'm not 100% sure of the flow rate but the pump I'm using is less than the max flow for the filter. There is a bluish glow from the UV so I believe it's working. My husband seems to think that it might be starting to clear a little but I honestly can't see much difference.

Algae colonies are still very small, 25 micron type range. You can't see them without a micro scope. Here are some pictures which I think are pretty cool.

You don't know what product, but do know the ad said 10-14 days? I'm a little drunk, but that still doesn't make a lot of sense to me. Do you just kind of remember the ad saying that?

36 watts for 4000 is probably OK if I had to guess. If the water doesn't clear turn down the flow.

One thing you can try that I do not normally recommend for frequent use, is a flocculant, like Eco-Floc or Clarity Max or other brands. They're fine when used sparingly and according to directions, and will help the UV along provided you have a pre-filter pad in your skimmer to catch the particles. The pad will need to be cleaned at least once a day while the pond is clearning. I've used it on occasion, and it works pretty quickly, one to three days. Leave the UV on, and once the pond clears, it should be able to stay ahead of the re-bloom.

May be time for aereation - I know it's a bit of expense, but great aereation can clean the pond of many ills. A friend of mine does it as part of his environmental( built a unti with 2 pumps and cleaned up a water run-off containment pond in 3 weeks - it was really nasty) business, I use it on my 635G pond a 2-3 time a month, run it overnight, also in the summer when the temp gets high it adds to cooling the water and keeping the oxegen level up.
Know on wood, but my pond has been healthy for several years. PLT

How often should the UV Bulb be replaced?