Don’t Add Beneficial Bacteria to Your Pond

The beneficial bacteria sold in stores are natural bacteria that are found in every pond; there is nothing special about them.

Pond water gets cloudy for a number of reasons. As organic matter breaks up into smaller particles, it becomes suspended and floats around making water cloudy. Algae and bacteria growing in water can also make it cloudy and algae can be a big problem in most man-made ponds. It grows when there is too much light and too many nutrients, especially nitrogen and phosphorus. If you reduce the level of nutrients, algae will not grow as well. So how do you reduce nutrient levels? Both plants and bacteria will keep nutrients lower and prevent algae from growing. Bacteria also decompose the suspended organic matter.

To make this work, you need to have enough beneficial bacteria. Manufacturers are quite happy to sell you these bacteria in a fancy jar with a fancy name: “beneficial” pond bacteria. One product I looked at cost $30 US for one year, to treat a 2,000-gallon pond (10 x 10 x 2.5 feet). They also have the super strength stuff at $60.

Natural pond with no pumps, filters

The beneficial bacteria being sold are natural bacteria that are found in every pond; there is nothing special about them. Everything in the pond including stones, the liner, plants and fish are covered with these bacteria. They are everywhere. The minute you finish making your pond, it already has billions of bacteria in it.

If the environmental conditions are right and there is a food source (i.e., organic matter), bacteria will grow and prosper. If conditions change or the food source runs low, they start to die off. Their dead bodies then become a food source for the ones that are still alive.

The manufacturers of beneficial bacteria would argue that high algae levels indicate that you don’t have enough bacteria. This might be correct, but the reason you don’t have enough is that the conditions are not suitable for them to grow. Adding some from a container won’t change that. If your natural bacteria do not grow, the purchased ones won’t either.

You can do things to kill off your bacteria, such as adding an algaecide, adding chemicals to adjust pH or passing the pond water through a UV system. Emptying your pond and scrubbing the sides to get it clean also removes them. Many recommend this, but it makes no sense at all. Why remove the slimy coating that is home to your natural water purification system?

If you did these things and killed your bacteria, it might make sense to add purchased bacteria to get your bacteria numbers up quickly. Or you could just wait a day or two for them to start growing on their own.

Keep in mind that adding chemicals like copper-based algaecides are long-term problems. The copper does not go anywhere, unless you do a water change. As long as it is in the water, it will harm the bacteria. Maybe this is one reason that companies who sell algaecides also sell beneficial bacteria and recommend you add them weekly. Their algaecide keeps killing off the bacteria, so you have to keep buying more bacteria.

One popular product contains 1 billion bacteria per gram. That sounds like a lot, but one gram of healthy soil – the weight of a paperclip – can also contain 1 billion bacteria. If you feel the need to add bacteria, just add a pinch of soil.

Buying beneficial pond bacteria is a waste of money. The bacteria you already have are just as beneficial as the ones you can buy. Stop using chemicals and UV treatment systems in your pond and start enjoying the benefits of a natural pond which is designed to keep bacteria happy, and algae levels low.

Robert Pavlis is a Master Gardener with 40 years of gardening experience, is owner and developer of Aspen Grove Gardens, a six-acre botanical garden featuring over 2,500 varieties of plants. A popular and well-respected speaker and teacher, Robert has published articles in Mother Earth News Ontario Gardening magazine, a monthly Plant of the Month column for the Ontario Rock Garden Society website, and local newspapers. He is also the author of widely read blog, which explodes common gardening myths, and, which provides gardening and garden design information.