How To Go About Cleaning A Garden Pond

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It's probably not unusual for the topic of pond cleaning to be the final straw for anyone thinking about constructing a garden pond. The whole idea is overwhelming and counterintuitive: Since when does anyone clean a pond? What are you going to do, take the water out and scrub it down? Well, yes, but only if you must.

Of course, what we're talking about here are small ornamental ponds you would find in a residential garden, around 150 square feet on average. Velda, a prominent European manufacturer of pond-related products, shares that a typical koi pond measures 11 feet by 16 feet, includes some aquatic plants, sometimes has fish like goldfish or koi, and typically has a liner.

Such a pond is not a closed system, of course, so it interacts with the world. As a result, it gets "dirty" and has to be cleaned from time to time. The things that make you think your pond needs cleaning are often symptoms of the chemical and ecological state of your pond — dark muck on the pond's bottom, an overgrowth of weeds, water green with algae; and in cases where things have gone a bit too far, even an unpleasant odor. We'll tackle all that, but first, let's look at what's happening beneath the surface. If you can make yours a healthy pond, it will require less cleaning in the future, which will make for happier fish, plants, and pond owners.

The Penn State College of Agricultural Sciences says the optimal pond ecological balance includes a "complete and balanced food web." There are a lot of ways this web can get out of balance. Alongside excess nutrients, insufficient aeration is the other major cause of ecological imbalance in a garden pond. And aeration is one of the major approaches to handling a large nutrient load. The excess of nutrients in the water is often caused by fertilizer runoff, manure, leaves, grass clippings, fish overpopulation, and many others. This material blocks light, which inhibits processes that produce oxygen in the water consumed by algae.

Light is the other key part of the balance equation. In fact, one of the key ways murky water harms your pond is by preventing light from getting where it's needed. Low light penetration reduces the amount of oxygen, creating murkier waters.

It's tempting to think you can simply control some variables (the presence of a shade tree, the fertilizer used on your lawn, the leaves and grass that find their way into the pond) to control light and nutrient load. But what you're confronting isn't just human choices; it's also the natural tendency of systems like pond ecosystems to change. Eutrophication is a natural process and is part of normal pond life, according to Pristine Waters. Eutrophication, the natural buildup of nutrients such as phosphorus and nitrogen, is always at work and must be dealt with.

In the fight over whether it's necessary to empty a pond periodically for cleaning, the sides hold unexpected views. The more scientific community seems to focus on the equilibrium that can be achieved by leaving a healthy pond alone, while the landscape-minded gardening community is prone to the more dramatic approach of draining, cleaning, and refilling ponds. Smack in the middle are pragmatic experts like those at Pond Informer, who argue that very limited water replacement in spring and fall is the right approach.

The Pond Place of Michigan recommends a 25% water change unless you have more than 1 inch of muck at the bottom of your pond, in which case you should do a complete water change. A complete water change is very close to starting over. It is a huge strain on your plants and fish, and might even be impossible if you have a large pond.

Chloramine is in water delivered to over 20% of American homes (via the EPA) and is more challenging to deal with because it doesn't evaporate quickly as chlorine does. This leaves you with the chemical fixes of activated carbon and water conditioners/dechlorinators specifically designed to handle chloramine. Keep in mind that removing chlorine and chloramine via activated carbon filtration is a slow process (how slow depends on the type of carbon, the size of your filter, the capacity of your pump, etc.), and so it might not be appropriate for any but the smallest ponds unless you can filter the water before introducing it to the pond.

Pay close attention to the amount of conditioner or activated carbon required to dechlorinate your pond. The popular Pond Guy brand of activated carbon treats 1,000 gallons, about enough for a 6-foot by 8-foot, 3-foot-deep pond, according to Hartz, and retails for $80. You might require three times that amount for an average-sized pond. Nualgi Ponds recommends replacement with rainwater. If you can store enough water, this is a good solution that bypasses the dechlorination process altogether.

Some mechanical cleaning will always be necessary with an immature pond or a pond that is even slightly out of balance. But once you rule out drastic water replacement, almost everything you do to make your pond healthier becomes a cleaning method of sorts. Filtration is one key approach. This broad category includes mechanical, biological, and UV (clarifying) filters, often combined with each other, per Envii Pond Klear. Mechanical filters like waterfall and canister filters are important components that take our debris in bulk and reduce the load on your biofilters. Biofilters include everything from bioballs to naturally filtering plants, like hornwort, soft rush, water lilies, and cattails (via Pond Informer). UV Clarifiers are often combined with canisters and other filters, and are effective at clarifying water by killing algae. Note that they do not remove algae, so effective clarification of water requires mechanical filtration as well.

Chemical alterations are another broad category of pond maintenance methods. This can include aeration, which can be facilitated by wind, waterfall or flowing water features, or mechanical aeration devices. Additives like gypsum can be used to clarify water. If you have low water hardness and an issue with clouding by suspended clay particles, gypsum might help. It's commonly understood that gypsum, being neutral, will neither raise nor lower the pH of water or soil, but there have been studies that show gypsum to have a mild effect on pH (via Soil Science Society of America). Epsom salts, alum, and limestone can similarly clarify turbid water, but these have a strong effect on water pH that might not be desirable (via Texas AgriLife Extension). 

Grass carp are used as a biological control mechanism to manage aquatic plant overabundance, according to the University of Florida. They naturally prefer problem plants like hydrilla and pondweed over cultivated plants like water lily and cattails. Just note that they can reduce water clarity while shifting available nutrients from plants to phytoplankton in the pond. You can acquire triploid (non-reproducing) grass carp with a permit in many states. 

In most cases, you would drain a pond by the simple expedient of a pump of one sort or another. A small pond or a slow drain would only require a slow method like siphoning, manual pumping, or perhaps a solar-powered pump, says Pond Academy. Electric submersible pumps are a good choice for draining moderately sized ponds, as are vacuum systems that also feature drain capabilities. For larger ponds, high-volume gas-powered pumps with 2-inch inlet and discharge hoses (or larger) might be called for. We'll assume a higher-volume pump, but note that a slower pump might really draw out some of these processes.

Start with some maintenance. The more leaves, muck, weeds, and debris you can move, the less your pump will have to deal with, and the less time your fish will spend out of their pond. Drain the water using the pump of your choice. If you have fish, start by filling the tank you will use to temporarily house your fish while you clean. Keep them in the shade, and don't keep them in your temporary tank for more than a few hours, Aquascape warns. Early in the process, try to pump this water from the surface of your pond, not from the mucky bottom. Discharge the water into your garden, lawn, or landscape to make use of nutrients suspended in it. As the water level drops, move the pump's inlet to the deepest area of the pond.

After draining and refilling your pond, the task of reintroducing any removed fish becomes your priority, and it can be a delicate process. New pond syndrome is a common set of issues with newly filled ponds, according to Nualgi Ponds, and these can also be introduced via a substantial water change. While experts might recommend a slow process for setting up a pond and coping with new pond syndrome, you don't have that luxury with fish that have been temporarily removed.

First, this is not the time to add new fish to your pond. According to Hoffman's Water X Scapes, beneficial nitrifying bacteria will take four to six weeks before existing in numbers to handle the fish waste. Work as quickly as you can once the fish are removed so that acclimating them to the new water isn't adding huge stress to huge stress. Finally, work in the shade, and if you don't have shade, find a way to create some. Water can easily overheat in small containers when exposed to direct sunlight.

Now, if your temporary holding containers (let's call them "tubs") will float, which is ideal, put them in your pond and add pond water to the tub, perhaps ⅓ of the volume of water in the tub already. Add a small amount every five to 10 minutes for no more than an hour before gently releasing the fish. Being gradual is key; your goal is to equalize the temperature between the pond and the tub and get the fish used to the properties of the pond before being immersed in it.