FYI: As I've had the pond for almost ten years without any incidents other than a hungry heron (and have since covered the pond with netting which I ain't crazy about!!!)I was a bit leery of gunk accumulating on the bottom so I used someone on this Forum's method of additional filtration. Using a Walmart plastic 20 gal trash can with drainiage holes drilled 1" above the bottom of the front panel and high loft batten inside and using a spare pump I circulated pond water through it for a few days. I would also occasionally rake (bamboo) the bottom to stir up sediment. This was a very cheap and effective way to clean gunk off the bottom as evidenced by the crud in the batten. I'll continue using this method until the batten is relatively clean. Thanks for all the useful info I've been able to gather here over the years.

Karin

The primary way to spec a UV is flow rate, how fast water can go thru the filter. If water goes thru too fast the algae isn't effected by the UV. The max rate is determined by the UV power (watts) and the size of the water chamber. This is why the manufacturer provides the info.

From the flow rate you can deduce pond size but this is also normally provided by the manufacturer. If UV flow rate is too low compared to pond size the algae will be able to reproduce faster than the UV can kill them and the pond never clears even though you'd be killing millions of algae cells.

The best manufacturers provide lots of info. At least rates for sterilizer and clarifier. The clarifier rate is more subjective so I prefer to compare sterilizer rates when picking a manufacturer, but then use the manufacturer's spec for picking a specific model.

You say that you want a little more clarity. The question has to be what are you trying to clear out of the water? A UV light can only clear single cell algae from the water that could be causing a clarity problem. So question has to be do you have this problem? The easiest way to tell if you have this problem is to take a white coffee cup of pond water. In this cup you can see the actual color of the water itself. If the water has a green color or green hue than a UV is the way to go but it doesn't have a green color that you don't need a UV. I am guessing that you don't have green water. The next step is determining if you have colored water or particles floating in the water. The white coffee cup test will tell you what color the water is. If you take a clear glass of pond water and hold it up to the light you can see what is floating in the water.
Mike