How to Keep Water Quality High
in Garden Ponds & Water Gardens
When we think of water quality in our water gardens and garden ponds we usually think of two things: the 
water's ability to support aquatic life and its clarity. Lack of clarity is usually not a problem for aquatic life, but limits our ability to see and enjoy our koi and goldfish. The pond owner should be concerned with both of these aspects.
While it is true that you can keep goldfish and koi in garden ponds with no filtration, it severely limits the number of fish you can keep. In the wild, fish have large amounts of water so that toxins from their waste do not build up to dangerous levels. Most hobbyists will want to keep more fish than their garden ponds will naturally support. Goldfish and koi excrete waste into the water in the form of ammonia, primarily through their gills. Also adding to the problem are organic compounds from fish feces, plant matter, and soil that may flow into the pond.
In order to provide good water quality some form of waste removal must be provided. Two methods used in average water gardens and garden ponds are mechanical filtration, and biological filtration. Mechanical filters physically remove solids from the water by trapping the debris in some form of mat, brush, or sponge. Mechanical filters are effective but generally require frequent cleaning to remove the accumulated matter. Most biological filters are also mechanical filters depending on how they are used. The mechanical filtration in most ponds is in the form of a pond skimmer.
Biological filtration is the most effective method of removing toxins from water gardens and garden ponds by breaking down ammonia into nitrite and then into nitrate. This is accomplished using naturally occurring bacteria called nitrosomonas and nitrobacter. Ammonia is broken down in natural bodies of water, but we must greatly improve on mother nature because of our limited space in and around the garden pond. We must provide a very efficient place for the bacteria to live and thrive. In a biological filter this place is a material on which the bacteria is exposed to large quantities of food and oxygen. One of the best materials for accomplishing this is a fiber matting media which offers a large surface area for the bacteria to colonize and also a large void area to allow large amounts of water to flow through carrying food for the bacteria. PolyFlo Fiber Filter Media accomplishes this better than most other mat type materials. Another excellent filter material is SpringFlo Bio Ribbon. This material is more open thus requiring less frequent cleaning.
Filter materials that are too dense will clog and not allow the water to flow through. We can also increase the efficiency by adding concentrated solutions of bacteria and enzymes such as Microbe Lift PL and Microbe Lift NiteOut. Providing an abundant supply of oxygen to the bacteria by the use of air stones or aeration towers in the filter will also increase the efficiency. There are also other organisms such as Blood Worms which colonize in a biological filter and help break down organic compounds.
Biological filters in water gardens and garden ponds must run continuously during the season. If they are shut down for more than a few hours the beneficial bacteria will begin to die. A biological filter should be cleaned using dechlorinated water if possible to avoid removing or killing the beneficial bacteria. Also the filter should not be over cleaned, rinse the media only enough to allow good water flow though the filter. The brown stain on the filter media is the living bacteria.
The nitrates that result after the breakdown of ammonia and nitrites are food for the plants or food for the algae if plants are not available. If you keep goldfish or koi and no plants you will also need to do partial water changes to remove the nitrates and other organic compounds from the pond water. If you keep sufficient numbers of aquatic plants, large water changes are usually unnecessary although small water changes of approximately 10 to 20% every 3 to 5 weeks can be beneficial.
At certain times of the year or if the balance of fish, plants and biological filter is off you may still experience green water in your garden ponds or water gardens due to a build up of single cell algae.
The best method of guaranteeing clear water against this problem is through the use of an ultraviolet sterilizer. This device uses a small germicidal UV lamp that is placed in a pipe to allow water to pass all around and will give a near 99% reduction in algae when properly sized to the pond. However an ultraviolet sterilizer must not be used without adequate biological filtration as the dead algae still needs to be broken down by the filter. UV will not help with string algae, for this we recommend Algaway. Also strive to achieve a balanced system using the methods below to keep string algae to a minimum.
There are many types of algae. There are different colors and textures. The green velvet type that grows on the sides of the pond is a very beneficial type of algae providing oxygen and food for goldfish and koi. This algae also gives a more natural appearance to garden ponds and water gardens. We get some calls asking how to get rid of this type of algae. Our answer is, if you can't tolerate this type of algae then you will need to get rid of your goldfish and koi and use a product called Fountec. Fountec is a product that will remove this type of algae and it is safe for plants and all animals except fish.
If you only occasionally have problems with algae or other suspended particles which interfere with water clarity in your garden ponds or water gardens then you might consider a flocculant. This type product works by causing particles in suspension to clump together and then fall to the bottom of the pond where it must then be removed by siphoning or vacuuming from the bottom, or a mechanical filter can be used to remove this debris.
Another useful product to aid in improving water quality in garden ponds and water gardens is a packaged bacteria and enzymes combination that will break down sludge and other organic compounds. Microbe Lift Sludge Away will help reduce organic buildup and sludge..
For your fish to be healthy and also to help with the control of algae, the pH of the garden pond water needs to be monitored using a pH test kit. The pH should be between 6.8 and 8.5 with the ideal being 7.2 to 7.8. Unless the pH is below 6.6 or above 9.0 then it is usually best not to try and adjust it.
How to Balance Your
Garden Ponds & Water Gardens
One major concern for water garden and garden pond enthusiasts is achieving and maintaining clear water. When water gardens and garden ponds are first constructed there is usually a rush to fill them up with fish and aquatic plants, but it is important to consider the natural process of these ecosystems. In nature a pond has a period of time for all the components to adjust and interact as the pond evolves. Although suspended algae in water gardens and garden ponds is to be expected most people want to keep it to a minimum. Constructed water gardens and garden ponds require help in order to avoid problems with excess algae. One method to control algae is to stock and arrange the pond with this method:
- Keep rain run-off out of the pond. It carries with it soil, fertilizers, and chemicals which will prevent the pond from balancing.
- If in full sun, shade 50 - 70% of the pond surface. Do this with the leaves of water lilies and floating plants. If your pond is in less than full sun, less surface coverage is acceptable.
- Use no more than one inch of fish per sq. ft. of surface area initially. After the pond has fully established or with well filtered water, more fish may be added. Feed only what the fish can eat in 5 minutes. Uneaten food feeds algae.
- Add biological filtration and an ultraviolet sterilizer.
- Remove any dead organic matter from the pond.