Like Oil and Water, Koi Ponds and Algae Don't Mix
So you have spent the time, money and patience building a beautiful koi fish pond only to have your hard work threatened by unsightly algae. This stringy green nuisance has plagued most koi ponds at one time or another. However, increasing the aerobic bacteria activity as part of your routine koi pond maintenance program will lead the reduction in excessive nutrients, resulting in a clearer, healthy koi pond.
When you get right down to it, algae is not the problem. It is a symptom of a larger problem, which is the nutrient level and oxygen content in your koi pond. Algae feed on the nutrients in the pond and when the nutrient level becomes high, algae will bloom and grow very quickly. Small amounts of algae in a koi pond is healthy, as it does add oxygen back into the water, however too much of a good thing is bad. To help remedy this problem, you need to remove the excess nutrients.
You can only do so much to limit the nutrients that get into your pond. The most common sources are koi food and the koi fecal matter. Since koi have to eat and they have to use the bathroom, your best bet will be to remove the nutrients once they get into the water. A good properly sized pond filter is the most appropriate way to deal with nutrients and waste produced in a koi pond. Many pond filters on the market today offer 2-3 types of filtration within one unit. Mechanical filtration is usually handled by a filter pad whereby larges pieces of waste and debris are trapped within the fibers where they can be broken down by beneficial bacteria. Further in the filter is an area for chemical filtration. In this area various types of media are used to help beneficial bacteria colonize. These bacteria will help process and remove ammonia and nitrite in the water which is lethal to fish. Finally as an added measure to some filters, a UV light will be presence. UV lights are especially effective and killing floating algae and bacteria before it inters the main filter area. When all 3 levels of filtration are combined, a clean and clear pond is very attainable.
The bottom line is, koi fish ponds are meant to be an aesthetic delight and a reflection of the owners vision and hard work. While not inherently harmful, algae is a nuisance and an eye sore that is not a welcome addition to a koi pond. However, with proper aeration and a quality pond filter, a koi pond can be a clean, beautiful, healthy oasis for the koi and the owner.