The external pond pump is one of your best water garden investments.
When compared to the smaller, less efficient submersible pond pumps, they work much more efficiently for medium (1000 gallons) or larger ponds.
Frankly with small ponds, you’re going to be doing a lot more cleaning and horsing around with a submersible and you don’t want to spend this kind of time with a larger pond. Use external pumps.
Combine With Water Filtration These pumps are ideal for combining with water filtration (many system simply sit inside the initial skimmer filter arrangement) They are also designed to work directly with the larger bio-filters and do not have one as an integral part of the pump.
Submersible Pumps Are Harder To Clean
Note that the smaller submersible pumps with their integral precleaning and bio-filter attachments are harder to clean and service. Heck, they sit on the bottom of the pond and if the pre-cleaner clogs up quickly you’re going to be wading and hauling it out every second or third day (or more often) to keep it working.
Note that if the filter ahead of the pump in the water flow clogs up, the pump will run hot. Too much debris on this filter and you’ll burn out your pump. And to make matters worse, the submersible pumps are often out of sight – particularly if your water is murky. You have no idea what’s going on down there.
In contrast the external pond pump works with a skimmer basket arrangement that can be visually inspected and cleaned without getting wet or having to do any wading.
Higher Flow Rates
Flow rates for external pond pumps range from 1000gph (gallons per hour) and up. The easiest way to calculate the size of pump you require is to calculate the total volume of your pond in gallons and then purchase a pump that is rated for that same volume.
In other words, if you have 3000 gallons of water in your pond, you want a pump that will move 3000 gallons of water every hour to keep the water moving properly.
If you are planning on having more fish than the rule of thumb of 1-inch of fish for every square foot of pond surface, then you’re going to want to run a larger pump to keep the water flowing faster and maintain oxygen levels. The danger in this of course is that if the power goes out, your fish will rapidly deplete the water of oxygen and they’ll start to suffer. Too long without circulation and oxygen replenishment and you’ll start to see dead fish.
Consider Two External Pond Pumps
Those who are operating their ponds for the primary purpose of growing fish may want to have two pumps running. This allows for a certain margin of safety should one the external pond pump burn out or break (inevitable with any machine I note).
Retrofit Can you retrofit an external pond pump to a smaller pond with a submersible?
Yes you can. It usually means installing a length of flex hose with a check-valve on the bottom so the water can’t run backwards out of the pump. Once you have the pump primed to run (some pumps are self-priming) the water flow will be fine. Do not run a non self-priming pump when it is dry.
I note if you hear the pump “whining” or working in a noisy way, it is working too hard. You may have too long a length of hose or have placed it too high above the pond and have made it difficult for it to work efficiently.
Tip: Hide the pump behind shrubs or plant larger, leafy perennials
You can find pond pump sizing and pricing here