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Natural Filtration for Indoor Ponds

There are many options for natural pond filtration.

By Stephen M. Meyer

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Q. I am very interested in your natural filtration system for indoor ponds. At present I am in the process of designing an indoor pond for my room addition. Any information you could give me would be very helpful.

A. When I began in the "pond business" years ago, a pondkeeper had to make practically everything. You had to be a plumber, electrician, carpenter, mason and engineer. Today, in contrast, there are a wealth of commercial products that bring pondkeeping within easy reach of those who do not relish the challenge of doing it on their own.

Tetra is one company that offers some very practical and effective items for budding pondkeepers. For the past several months I have been field-testing Tetra's (Brilliant G) Pond Filter. (Yes, I went out and bought one at a local store-- no freebies.) This is a large sponge filter specifically designed to provide mechanical and biological filtration for small outdoor ponds. It is ideal for indoor ponds.

The large cylindrical sponge has an extensive surface area. The telescoping neck allows the filter to be used in ponds up to 40 inches (about 100 centimeters) deep, though I would not suggest going much beyond 24 inches (about 60 centimeters). A weighted base (you add your own aquarium gravel) places the filter firmly on the pond floor. The snap-design locking mechanism that holds the sponge in place disassembles and reassembles quickly for easy cleaning of the filter.

Using Tetra's Luft Pump-G, a heavy-duty air pump, the company claims that the filter can deliver 400 liters (105 gallons) per hour. My tests showed that this is right on the mark for a new sponge operating at a depth of 22 inches (56 centimeters). However, after several weeks of operating — with weekly cleanings — the average flow stabilized at around 300 liters (80 gallons) per hour. This setup also aerates the water very nicely — an important plus for indoor ponds.

The Luft Pump, which has an adjustable air flow, is designed for outdoor use. Like almost all vibrating air pumps, it emits a noticeable buzz when operated at maximum flow with the filter at a depth of 22 inches. Outdoors, you would not notice it. Indoors, it can drive you nuts. You can build a little sound box using Styrofoam to encase the pump if the buzzing bothers you.

To increase the flow and turbulence across the pond's surface, I removed the Luft Pump and seated a Marineland Penguin Powerhead (#550) directly on the outlet tube. This produced a nice steady flow and no sound at all. With the powerhead's aerating feature in operation, the gurgling sound was still more pleasing than the buzz of the air pump.

One good reason to prefer this Tetra filter and Tetra Luft Pump combination is energy efficiency. My indoor pond's lava rock filter was driven by a small water pump. This 0.6-amp pump costs about $48 per year to operate. The Tetra filter with the Marineland Powerhead (0.17 amps) costs about $14 per year to operate. The Luft Pump (0.05 amps), however, costs a measly $4 per year.

Tetra says the pond sponge filter will handle ponds up to 1500 gallons (about 5600 liters), but that means, at best, only two pond volume turnovers per day. This strikes me as far too little for good biological filtration and aeration. I would strongly recommend this filter for outdoor and indoor ponds up to 200 gallons (about 750 liters). If your pond is larger, buy an additional sponge filter and an air pump/powerhead to drive it.

Having used this filter since April of last year, I can confidently say that in terms of simplicity, effectiveness, energy efficiency and convenience, this is an excellent filter for an indoor pond. As long as you stay within my recommendations concerning pond size, I think you will be quite pleased with this filter.

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