What's the difference between External Pumps and Submersible Pumps?

by: Demi Fortuna

External pumps are the type used for swimming pools, mounted on the ground above water level, with an attached basket to keep the intake clear of debris. Many pondkeepers, especially Koi enthusiasts, prefer external pumps because the ones that are specially modified for ponds are very quiet and very efficient, and the two inherent drawbacks of external pumps, that they are visible (and sometimes audible) and that their intakes need to be plumbed precisely, aren't much of a problem for them. Koi ponds typically have above-ground filtration systems which need to be screened anyway, so having to hide the pump too is no big deal. As far as plumbing goes, Koi ponds usually feature elaborate valving, filtration and bottom drains which require a talented installer; external pumps are relatively easily connected in comparison. Proponents of external pumps point out that they are also readily accessible for cleaning and maintenance. IMPORTANT! If you are thinking of using your old swimming pool pump, forget it! Those are designed for intermittent duty, not the continuous duty required in ponds, and are high-pressure and very power-hungry. Pumps designed for water garden use are so much more efficient, you'll typically recoup the entire cost of a new pump in one season with what you'll save off your electric bill.

Sea Horse External Pond Pump

Submersible pumps are by definition hidden from view (and hearing) underwater, and don't need any intake plumbing at all, since they draw water directly into the pump. Since they are easier to hide and connect, and are often less expensive than externals, they have become the most popular type of pump for water features, but they have their drawbacks too. Submersibles that sit directly in the pond, sucking up sludge, typically require more time and effort to maintain than externals. Clogged intakes are the number one cause of pump failure, so regular maintenance is critical, and since they have to be removed from the pond for cleaning, that can be pretty messy. That's why for ponds larger than a few hundred gallons, Skimmers that prefilter the water through a basket, pad or net and keep pumps accessible at the edge of the pond have become the industry standard. Since a Skimmer makes it easy to keep pump intakes clear and makes maintenance easy (and relatively clean), submersible pumps in Skimmers have become the most popular option for ponds.