Whether you are dealing with a pond that is a main feature in your landscape, or just a farm pond out in a field, monitoring water quality can have a huge effect on the ability of the water to sustain life. The water's pH level has a great impact on the overall health and vitality of fish, and it also determines whether certain aquatic plants can survive or not. High pH levels can be dangerous, and knowing how to reduce them is important when you want to maintain certain types of life in your pond.
The Associated Koi Clubs of America (AKCA) points out that testing is the first and most important step when trying to maintain a certain pH in pond water. Testing is most effective when results are, "plotted on graph paper over a period of several testings," as opposed to performing one single test. You can expect some fluctuation in pond pH over time, and multiple tests will prevent you from accidentally treating a problem when none existed. If, however, your series of pH tests reveal higher than normal pH (8.0 or above), then there are some basic steps you can take to improve the water quality.
Two Steps For Treating Alkalinity
The Pond Doc, an Internet resource for common pond water quality issues, points out that, "Simply lowering the pH is only a temporary fix to the problem. It needs to be stable." When you address your pond's alkalinity, then, you'll treat the problem in two steps: first, you'll need to lower the overall alkalinity of the water to safe levels, and then you'll need to stabilize the overall environment so that the alkalinity doesn't go right back to where it was.
Lowering the pH is simple and can be done without chemicals so long as the situation is not severe. In most situations, simply adding carbon dioxide (CO2) to the environment will lower pH significantly. According to William Wurts and Robert Durborow of the Southern Regional Aquaculture Center, carbon dioxide leans naturally to the acidic side, and can be added in several ways. Because it is exposed to CO2 in the atmosphere, rain water runs acidic. Using a rain barrel or finding a way to divert rainfall into your pond will provide a natural balance to high pH. In addition, this will save you from having to periodically fill the pond as evaporation occurs. Ground water also runs acidic, and if you have a well this can be used also. These are the best solutions because one of the principle causes of alkalinity in pond water is evaporation, which concentrates the natural pH-raising effects of concrete and limestone.
Finding a consistent source of slightly acidic water to add to your pond will do much to stabilize the environment. However, further efforts may be necessary, particularly when the pond bottom is newly poured concrete. Norm Meck, writing for Aquarium Life, notes that frequent aeration can have positive effects for pond waters that run either acidic or alkaline. In addition, certain bacteria provide a natural balance in the water due to their respiratory patterns. Healthy bacteria for pond water can be purchased from hobby shops and aquarium stores.
Opt For Slow, Steady Change
When treating any pH problem in pond water, Meck cautions that chemicals should only be used in emergency situations. Although fish and plant life can generally adapt to pH levels ranging from as low as 6.0 to as high as 9.0, they do not handle rapid changes well. A gradual solution such as that produced by progressively introducing slightly acidic water will allow all life forms in the pond to slowly adjust. You'll also ensure that no microscopic bacteria are harmed in the process, which will lead you to a stable, healthy environment in which plants, fish, and bacteria can live in balance.