A submersible pond pump is probably best in small water garden ponds, say below 800 gallons of water.

Normally we'll see them in the smallest of ponds (200 gallon range). No matter what the size of the pond, the pump must be sized to the pond and we're looking for a pump with a rated capacity equal to the gallonage of your pond.

So if the pond holds 500 gallons of water, the pump should have a capacity of 500 gallons per hour. Anything less will produce poor results and increased fish death.

Advantages Of Submersible Pond Pump

The advantage of submersible pond pumps is that they are fast to install. Plug'em in and drop 'em in. Away they go. Note that submersible pumps will often burn out if run out of water - never run the pump in the air

The advantage is that sometimes they come "bundled" with filters so it's a one-drop pond system. The disadvantage of this is that if you have fish in the pond, you're going to have to pull that pump almost every day to clean out the filter. You'll be amazed at how fast the filter (normally a sponge affair) will clog up under normal fish and plant loads in the middle of a hot summer. If you run the pump with a plugged filter, you're putting your pump under extra "load" (it's harder to pump when the inlet is blocked) and this will result in a shorter pump life. Short pump life quickly makes up any saving between putting in a larger pond or a larger filter/pump system.

The advantage of the average submersible pond pump is that it is quiet and you don't hear it running. The disadvantage is that if the seals break on an oil-cooled model, you're going to have oil in your pond. This happens more than you might think and this is why the often repeated recommendation is to spend a little more money and purchase a magnetic-drive submersible pump.

Certified Pump

Ensure your potential pump has the appropriate national certification and that it is a thermally protected motor. They normally will be but if you're buying off the Net, please understand that there are a lot of offshore pumps being sold and I'd recommend you purchase brand names rather than the cheapest. And do ensure the cord is grounded and that it is running on a ground-fault-interrupter (GFI) plug. The only shock you want is when you see how many fish a mature breeding pair can produce in a very small pond.

Corrosion Resistance

If you purchase a submersible pond pump with exposed metal shafts, ensure those shafts are treated for corrosion or that they are the newer ceramic shafts. Rust is not a good companion in ponds.

Ask about the seals and see if they are pond-rated for wear (there are different grades of seals) and pond water. Some seals are even rated for salt-water application so it's a good idea to get the pond supply dealer to pull out his book of product specifications or you can research the individual pump by googling its name.

If you buy a magnetic-drive pump, see if the magnets have been heat-treated so they'll stand the test of time and internal heat.

Check out the wattage and efficiency of the pump motor if you're buying a conventional pump. What may be a cheaply purchased pump may more than make up the difference in electricity consumption over a single season. Go with high-efficiency motors wherever possible. I note these motors also produce less pump-destroying heat.

You'll be able to find all kinds of "deals" on the Internet for purchasing a submersible pond pump.