The only true way to completely rid your pond of free-flowing algae (green water) and keep it clear from algae is to install an Ultra Violet Water Clarifying Sterilizer Unit, affectionately known as a "UV".
A UV is a bulb inside a PVC tube that is protected from water by a tube of glass. Water flows through the PVC tube and passes by the long bulb so that the ultra violet rays emitted from the bulb can sterilize microscopic algae that flows along with the water. This prohibits reproduction and growth of the algae and it quickly dies back. A UV is not effective against string algae because this type of algae attaches to the sides of the pond and rocks in the waterfall and does not pass through the light.
The strength of the UV that should be installed is solely dependent on the amount of water you are trying to clear. Use the following table to determine what size UV is needed for your pond:
Minimum Gallons Maximum Gallons Wattage 0 400 8-watt 400 800 15-watt 800 1500 25-watt 1500 2500 40-watt 2500 4000 65-watt 4000 5000 80-watt 5000 7000 120-watt
If your pond size is on the borderline most the time you’ll want to bump up to the higher wattage UV. For example, most ponds receive a fair amount of sunshine during the day. Sun promotes growth of algae and makes the UV work harder. If you have a 1500 gallon pond out in the sun you’ll do much better by investing in a 40-watt UV rather than being conservative and going with the 25 watt.
A UV is installed into the PVC line or flex hose that carries the water from the pump and through the system and must be installed outside of the pond and not submerged. Locate it preferably after the biofilter.
The rate of water as it flows through the UV will have a direct bearing on how effective the UV is on the algae kill rate. If the water is flowing too quickly through the unit, the algae is not given enough exposure to the ultra violet rays and the unit may not work effectively. For that reason, it’s a good idea to install the UV on a line that by-passes the main line and allows only a portion of the water to flow through it at a much slower rate. We prefer to use PVC and tee the main line, placing gate valves where they can effectively slow down the water flow in specific areas. The UV line that was tee’d off from the main line can then be rejoined to the main line or returned to the pond through a separate return line.
Do not run your UV while your biofilter is trying to seed. It takes time for the bacteria to seed in a new filter. UV’s will kill some free-flowing bacteria making it more difficult for the bacteria to grow inside the filter. Though we all hate that green water it’s best to put up with it until the bacteria in your biofilter has had a chance to fully develop. Green water doesn’t kill fish but lack of bios does.
Go HERE to find more information about UV's. We understand how difficult it can be to properly size and install an Ultra Violet Water Clarifying System. The advantage of purchasing the system through us is that you can benefit from our experience. We will be happy to help you with the installation by offering our free in-house consultation with every step of the buying and installation process.