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Each manufacturer will have a slightly different recommendation. Also do you want it just to kill algae (clarify) or to sterilize (kill bacteria) as well?
Sterilization requires more wattage.
IMHOand a place to start you would be some where in the 4 to 9 watt range. I would go with the higher side. The lamp degrades over time.
The key is to rate the flow through the unit properly. If you are adding the UV to an existing line size it to the flow in the line. If the flow rate through the unit is too high the UV will be ineffective.

Sheryle,

Not sure who's UV unit your planning to buy, but UV's can be used either as a sterilizer or a clarifier. As a sterilizer the UV will keep your pond crystal clear in addtion you'll have the benefit of bacteria control which keeps your fish happpy and healthy with less risk of disease. If properly sized as a sterlizer you should see crystal clear water in 3-5 days (sometimes sooner).

As a clarifier, the pond will have a green tint to it, unless you have 50-70% plant coverage or your pond is in full shade.

Functioning as a sterilizer or a clarifier is determined by the size of the unit you purchase as compared to your pond size. Also flow rate through the UV is very important in terms of its effectiveness. Optimum flow rate is to turn over the volume of water once every hour or a minimum of once every other hour.

I'm familar with Aqua UV. The following is their sizing recommendation for a 1000 gallon pond:

- As a sterilizer a 8W UV can support a 5-200 gallon pond. Used as a clarifier the 8W UV can support up to a 1200 gallon pond. Maximum flow is 1000 gph.

- As a sterilizer a 15W UV can support a 200-500 gallong pond. Used as a clarifier a 15W UV can support up to a 2000 gallon pond. Maximum flow is 1800 gph.

- As a sterilizer a 25W UV can support a 500-1200 gallon pond. Used as a clarifier the 25W UV can support up to a 4000 gallon pond. Maximum flow is 2000 gph.

The next logical unit they offer is a 40W UV which as a sterlizer supports ponds from 1200-2000 gallons and up to 6000 gallons as a clarifier. Maximum flow rate is 3000 gph.

As a clarifier it appears you a 8W unit will work. As a sterlizer it appears a 25W unit will work.

Decide which brand you want to purchase and view their Web site. Most have sizing charts which can determine which unit is right for you.

Hope this helps.
Steve

I would use the 2000 gph pump. Remember the value your probably looking at is the manufactures maximum flow rate of the pump at zero head (meaning at the surface of the pond without any pipe work or fittings attached). Depending where the pump is located with respect to the pond (length of pipe including elbows if used) and height of the pipework where is breaks the surface (head) will have an effect on the flow rate.

The UV can be located before or after your bio-filter. If your able to I would locate the the UV filter after the bio-filter in order to avoid the possibility of a large particle from possibly breaking the quartz sleeve which can be fairly expensive to replace.

You can install a ball valve on the output side of the UV to control the flow rate if necessary. This way if you find that the flow rate from the pump is too great causing the UV not to be as effective, you can restrcit the flow going back into the pond so the UV can work more efficiently.

Hope this makes some sense and is not too confusing.

Steve

yes thanks,
and use the 40w uv

sheryle

You can use the 40W unit or probably even get away with the 25W unit. My orignal 1200 gallon pond I used a 57W unit from Aqua UV. Worked great. When we did our pond expansion we added a 120W unit in series with the 57W unit and installed a ball valve on the output side of the UV to control the flow.

Just remember the UV cannot differentiate from good bacteria or bad. So when adding beneficial bacteria turn the UV off for 48 hours to give a chance for the bacteria to colonize in your bio-filter. Some medication will may also require turning the UV off for a period of time.

Also as Murph indicated the lamp deteriorates over time. Aqua UV recommends changing the bulb every 14 months.
Steve

Yes you can. You should try to clean out what ever algae that died. If not this will only feed as nutrients for the next bloom. I add one tablespoon per 1000 gallons each week after a water change. During the hot summer months I double the dosage.
Steve