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To a Trickle

The flow rate of a pump is only as good as the flow through the inlet.

By Stephen M. Meyer

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Q. I have been keeping koi in a 1400-gallon pond for many years. Until recently the pond filter and waterfall system was powered by a submersible CAL Engineering pump. When it burned out (after many years of continuous use) I replaced it with one of those new high-efficiency pumps made by OASE. The pump seemed to offer the same pumping rate, but at one-third the electrical usage of my old pump. That would shave about $10 a month off my electric bill, and since it came with a three-year warranty I figured it would pay for itself and then some.

Well, things are not going so well. The new pump does indeed match the flow rate of my old pump, but only for a few hours. After about six hours the screen that covers in impeller clogs with muck and algae and the flow is reduced to a trickle. I have had the pump a week now and I have to clean it three times a day! My old CAL pump required cleaning only every few days.

The OASE pump is not suitable the way it works now. Any suggestions?

A. The new high-efficiency submersibles, such as the OASE and Tetra Pond pumps, really do save money on electricity. During the six "winter" months that my koi are inside, one of these pumps saves me between $80 and $100 on my electric bill compared to standard commercial submersible pumps.

Fortunately, my indoor system is free of the kind of muck and algae that can clog pumps in outdoor ponds. But when I move my fish outdoors and transfer the pump to drive the filter and stream system, I run into the same problem you describe.

These high-efficiency pumps get some of their added pushing power from specialized impeller designs that, unfortunately, make them prone to fouling by fairly fine matter. Therefore, these pumps come with very fine mesh screen covers over their inlets.

And as you discovered, these screens do their job well. They stop even tiny pieces of hair algae from entering the pump chamber. So, unless you have an immaculate pond floor, they clog up pretty quickly.

There are two possible approaches for addressing your problem. One is to remove the screen cover and attach a more substantial screening device to the inlet. By substantial I mean a fine mesh screen of much larger surface area than the simple inlet cover that comes with the pump.

There are several good supplementary in-pond screening filters available commercially. Danner Manufacturing (makers of Supreme filters) offers two inexpensive models commonly available in aquarium stores. The Pondmaster 1000 (you will need several ganged together) is a modular tray design. It has a 12-inch by 12-inch surface area on the top side of the tray. The filter tray sits on the pond floor and draws water in through the top. This reduces the amount of pond floor muck that gets picked up.

The Universal Pond Filter is a drum (again, you will need to gang several together). This filter should be suspended mid-water because if it sits on the pond floor it will pull debris in very quickly.

There are many similar models available by other manufacturers. In either case, I suggest you remove the filter pad that comes with these unit and replace it with ordinary cloth window screening. Window screening provides all the mechanical filtering necessary without the constant clogging. And it is very easy to rinse clean.

If you are a do-it-yourself person, you can make your own screen filter. Buy a heavy-duty bucket (a dark color will be less visible in the pond). Drill a few ¼-inch holes along the bottom edge to allow water to seep in and out. Notch the top to allow the pump outlet hose and cord to fit below the bucket rim. Now place the pump (with the original screen cover in place) in the bucket, run the outlet hose through the notch, and cover the open end with window screening. You can secure the screen with a large rubber band.

Now submerge the whole assembly in the pond, being sure that the bucket stands up. This system will draw water from mid-pond and keep the muck out of the pump. As far as I am concerned, this works just as well as fancier commercial filters.

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