Thumb through any book or magazine about ornamental ponds, and you will come across page after page of beautiful photographs; clouds reflected on a pond’s surface, water lily pads floating among tropical blooms, and colorful Koi dancing in crystal-clear water. What you don’t see are the mechanical devices that operate out of sight and out of mind to create those scenes. Without them, the typical ornamental pond rarely would appear to be more than a mud puddle.

This article examines “must-have’ gadgets and gizmos for successful backyard ponds. When it comes to pond equipment, three questions should be foremost in your mind:

1. What do I need?   2. Why do I need it?    3. How do I choose the right product for my needs?

Pump it Up:  If water is the lifeblood of the pond, then the pump is the heart. In the course of circulating water through the pond, the pump maintains even water quality, temperature, pH, etc. throughout. The flow across the pond surface, and perhaps over a waterfall or through a stream bed, expels carbon dioxide into the air and absorbs oxygen. The continual circulation bathes nitrifying bacteria on the pond walls, pond floor and other biologically active surfaces with nutrient rich water. This “filters” because the food that the bacteria crave is poisonous to the fish that produce it.

The pump is literally the keeper of life and death in a pond. That is why you should choose carefully when you buy one.

Flow Capacity: The most important characteristic to consider is the pump’s flow capacity. Plan on a recirculating rate between on-half and one entire pond volume per hour (assuming a pond volume that is less than 10,000 gallons). In other words, a pump serving a 1,000 gallon ponds should move at least 500 gallons per hour through the pond. If you plan to have a lot of fish in the pond, Koi in particular, you should err on the high side of this recommendation.

You might think that all you need to do is match the maximum flow rating listed on the pump box to your desired flow rate, and you’re done. Sorry, it’s not that easy. The flow capacity listed by manufacturers is usually for one foot of “head”, that is, the flow that will emerge from a pipe one foot long pointed straight up.

What you need to know is the flow rate generated by the pump after it has pushed the water through the pipe system, all the way around the other side of your pond and up to the top of your waterfall, streambed, filter box or fountainhead. For this you need the flow versus “head” chart that goes with the pump. Every pump model is different. (Ignore horsepower ratings; they communicate no useful information). If no such chart comes with the pump, ask the retailer he should have a chart book for that specific pump. If you can’t get this information, don’t buy the pump.

The flow versus head chart tells you what flow rate you can expect from the end of the pipe, taking into account resistance inside the pipe and how far the pump has to push the water uphill. For our purposes, the latter quantity, the vertical distance above the pond surface that the water must flow before it exits the pipe, will be the most important consideration. Most waterfalls sit between 2-3 feet above the pond surface. Some streams, however, might begin 30 feet or more away from the pond and rise 5-10 feet at its highest point. How far above the pond surface (vertical distance) will you place the pipe outlet?

Add 2 feet to your planned vertical distance, and then look up the expected flow rate for this “head” value on the chart. It should be in gallons per hour. (If it is in liters per minute, multiply that figure by 15 to get a rough estimate of gallons per hour.) Multiply the gallons per hour flow rate by 1.7; this is the approximate maximum pond size in gallons that this pump should service. Choose a pump that yields a flow versus head figure that matches your pond volume or slightly exceeds it.

A good idea is to purchase a slightly larger pump because flow versus head charts assume that you keep the pump inlet free and clear of debris, which isn’t realistic in a pond. After a few days of operation, suspended particles from debris (commonly referred to as “gunk”) accumulates on the coarse mechanical filter screen and around the pump inlet which will effectively cut the flow rate through the pump.

Likewise, gunk will build up on the inside of the piping over time, further inhibiting flow. Taking this into account and assuming a reasonable biweekly maintenance schedule, I recommend opting for a slightly high capacity pump.

The simple rule for sizing the pump assumes that you use 1-1/2 “ diameter PVC pipe for all pumps with outlets smaller than 1-1/2" and a 2" pipe for pumps with a 1-1/2" outlet. Connect the pipe to the pump with a connector that is threaded on one end (to screw into the pump) and is a slip joint on the other, into which you glue the PVC pipe. Using smaller diameter pipe results in a serious loss of flow due to friction in the pipe.

Energy Efficiency: Pond pumps should run 24 hours a day, seven days a week from spring through fall in most areas. Intermittent operation is a prescription for a water quality disaster, with wildly fluctuating pH and dissolved oxygen levels. Continuous operation of even a small pump can add several hundred dollars to your electricity bill each year. Therefore, of the pumps that meet your flow need, choose the one that has the lowest wattage (or amperage) rating. Energy-efficient pumps can be several times more expensive than ordinary pumps, but they will save you far more money in the long run.

Submersible vs. External Pump: Both designs are reliable and effective. Choose the one that fits your pond design. If you decide on a submersible pump, stick with those designed for pond use. Do not use an ordinary sump pump; they are not built for continuous duty.

Filter Fundamentals:  There are probably hundreds of commercial pond filters available today. Selecting the one that is right for you depends on many variables specific to your pond. Lets review the basic characteristics of the available alternatives to see which one best addresses your needs.

Our interest in pond filters is limited strictly to mechanical and biological filtration. Mechanical filtration refers to separating the gunk in the water column. Biological filtration means setting up a dedicated medium (a filter pad) where nitrifying bacteria can grow and remove ammonia from the water.

Unlike aquariums, pond filters rarely utilize chemical filtration (say, using activated carbon) because it is ineffective in the outdoor environment. The carbon is quickly covered with a bacterial and algal slime that prevents chemical absorption. (There is one exception: Foam fractionation, similar to that used in marine aquariums, is a chemical filtration technology that does work quite well in ornamental ponds. The device is very complex and is useful only in heavily stocked Koi ponds).

Foam Filters: The simplest “all-in-one” pond filters are the foam block units that attach directly to a submersible pump’s inlet or encase the pump. These filters provide adequate mechanical and biological filtration for small ponds (less than 250 gallons). They also serve to protect submersible pumps by keeping debris from jamming pump impellers. (External pumps should be equipped with an in-line filter basket for mechanical screening of large debris.)

Simplicity has its limitations. Foam filters designed for direct use with submersible pumps clog quickly after several weeks in the pond. They might need daily cleaning to flush the gunk from the foam. In this respect, designs using thin, coarse pads are far better than those using thick pads with tight cells because they clog less often (which translates to less maintenance) and they actually provide better biological filtration (dissolved oxygen levels remain fairly high throughout the entire thickness of the pad).

Skimmers: Larger ponds, especially those that are more than 500 gallons, should have more sophisticated filter designs that separate mechanical and biological filtration components. In other words, larger ponds must have a skimmer box, a box placed outside the pond with an inlet that sits partially above and partially below the pond’s water surface. An opening through the pond wall allows water to flow out over into the skimmer, carrying floating and suspended debris. Inside the skimmer box, mesh nets, screening and layers of coarse foam pads separate out the gunk. Cleaned water then flows into a second chamber of the box from which it is pumped out and around the other side of the pond. You can put a submersible pump in this second chamber (a common approach) or attach an external pump through the skimmer box side wall.

Skimmers for ponds come in several varieties. I suggest getting the largest skimmer that you can afford. At the very least, get one that serves at least twice the pond capacity recommended by the manufacturer. For really large ponds (several thousand gallons), you can install several of these skimmer devices each with its own pump or gang them together using one large external pump.

Paper Cartridge Filters: More exacting through mechanical filtration can be achieved with paper cartridge canister filters, which look somewhat like a large aquarium canister filter. This system sits out side the pond with a paper cartridge (similar to those used in hot tub filters) held in a sealed canister.

These filters are very effective in removing smaller suspended particulate and can help screen planktonic algae that make the water green. You won’t need paper cartridge filters in a typical garden pond with a few goldfish (it would be overkill) but they can be quite useful in dedicated Koi Ponds with large fish loads. Paper cartridge canister filters are fairly large and require some creativity to hide. You can try hiding them behind a fence, shrubs or perhaps inside a garden shed.

Fountains of Youth:  An entirely different return is a fountain head. These devices can aerate pond water effectively as well as produce wonderful aesthetic effects. Obviously, the more spray nozzles you have and the finer the spray, the better the aerating capacity. In other words, cherubs spitting in a stream of water do not do much for the fish. Good fine mechanical screening is essential to prevent fountain heads from clogging. Avoid copper fountain units; with acid rain and acidic water, they pose serious health risks to fish.

GFIC and UV’s:  All pond devices that use electricity should be plugged into a ground fault interrupter circuit (GFIC) without exception. GFIC outlets detect minute current flows to ground and open the circuit to prevent electrocution. It could save your life. Moreover, should a ground fault occur in a submersible pump, it will keep your fish from being fried.

An ultraviolet sterilizer is by no means a must, but it does serve a purpose in some ponds. Exposing flowing pond water to UV light kills bacteria, inhibits unicellular algae growth and keeps the water clear. When all else fails, UV light will clear the water. A UV sterilizer is especially helpful for people who inherit a pond whose design precludes more desirable contemporary approaches to anti-algae management such as locating it in a shady area or designing it with an integral biological filter.

There is no evidence that continuous use of a UV sterilizer reduces fish diseases in ponds, nor is there evidence that it harms beneficial bacteria. So the choice is yours.

The best types of sterilizer are those with an in-line design where water is pushed through a pipe that has a UV light running down the center of it. If you purchase a UV sterilizer, make sure to get one where the water wraps around the bulb, which is protected by a quartz sleeve.

UV sterilizers come in many different sizes and all have individual ratings. It is best to select a UV sterilizer with a minimum flow rate. So if your flow rate is 200 gallons per hour, select a UV unit where 200 gallons per hour is at the lower half of its range. It is best to get one that is nominally larger than the size recommended for your pond by the manufacturer.

Deepfreeze (something we in the south don’t have to worry about) If your pond freezes over for more than a week or two each winter, then invest in one more deicers. These devices float on the pond surface and create an open hole throughout the winter.

The obvious value of a deicer is that it allows for continuous gas exchange between the pond and the atmosphere after ice forms on a pond surface. Most fish that die while being over-wintered, probably got sick because of toxic buildup of gasses in the pond water when ice sealed the water surface/atmosphere interface. Sold in 500 and 1,000 watt sizes. I recommend the larger for all ponds and several deicers for ponds with extensive surface areas.

Testing 1,2,3:  Yes, water quality test kits are an essential pond gadget. You should have test kits for pH, ammonia, nitrites and dissolved oxygen. Nitrate testing is irrelevant in ponds. If your source water is chlorinated, then a chlorine test kit is essential. A thermometer also is a necessity..

Water testing should be conducted once a week and whenever things just do not look right or when a sudden change occurs. For example, test the water if the pond suddenly greens up or if it suddenly becomes crystal clear.

Final Thoughts:  I always recommend buying pumps, filters and other gizmos at least one size larger than recommended by manufacturers.

The capacity numbers offered on commercial products, flow rates, bacterially active surface areas or UV radiation flux are “clean water” numbers derived in sterile factory settings. Outside, things are far messier. Chemical scale buildup, for example, can significantly cut the heating efficiency of a deicer. Dirt, debris and bacterial and algal growth reduce the capacities of all kinds of pond equipment.

You can greatly reduce your maintenance headaches by over sizing your pond equipment. Remember: Most of these devices shouldn’t need to be replaced for many years.

My one basic recommendation for maintaining pond equipment is: Check and clean early and often. Do not assume that if the fish are not floating belly up, all is OK. Pond systems can fail catastrophically (as in a pipe burst), but often they fail incrementally (as when a fish dies under a water lily pot and the rotting carcass pollutes the water). It might take a week or more before declining water quality causes your fish to show signs of illness and by then, things are very serious.