Why Is My Water Green? And What Can I Do About It?

By John Tinius
reprinted form Koi USA

One of the most frequent problems with our ponds is green water. As everyone knows, green water is the result of algae growth, this article will look at some of the basics about algae and how to eliminate them.

WHAT IS ALGAE?
Algae is one of many plants belonging to the subdivision thallophytes found in both salt and fresh water. Algae comes in many forms including both free-floating and anchored, or attached. Algae comes in many colors including green, brown, blue, and red. Algae is carried through the air by spores and may locate in any body of water.

ALGAE NEEDS
Algae has several basic needs. Understanding them and how to eliminate them are the key to having clean, clear water.

A. FOOD: Algae feeds primarily on nitrates and phosphates in water.
B. LIGHT: Algae needs light to grow and reproduce.
C. TEMPERATURE: Algae growth is faster in warmer water and slows as temperature decreases.
D. WATER QUALITY: There are many varieties of algae that exist under a large range of conditions. However, any water that is of such poor quality that it will not support algae growth will also not support fish life.

ALGAE CONTROLS - SOLUTIONS
The three basic ways to rid your pond of algae are:

A. ELIMINATE FOOD
B. ELIMINATE LIGHT,
C: KILL ALGAE.

Algae can be eliminated by removing either food or light. It is not necessary to remove both. To understand how to literally starve out algae we need to go to the basics of biological filtration and how algae food is produced. Bio-filters consist basically of a bed or strata on which bacteria grow. That's it. Don't let a lot of complicated systems or designs confuse you. That's what is really happening inside. Fish produce ammonia as a waste product. In the presence of an oxygen-rich environment, aerobic nitrosomona bacteria break ammonia down to nitrites. Nitrobacter bacteria break nitrites into nitrates. Nitrates are algae food. Through a similar process, phosphates are also produced. Phosphates are also algae food. By keeping nitrates and phosphates at low enough levels. algae will starve. A good bio-filter keeps these algae foods under control. I know even a pond with a well- functioning bio-fllter may go through bouts of green water This is mainly caused by phosphates reaching levels where algae life can be supported. A healthy bio-filter will react by increasing bacteria that can consume phosphates and, in time, will clear itself, if the system is not overloaded. A regular program of 10% water changes each week helps keep nitrate and phosphate levels under control. However, filter size, fish load and the amount of fish food used all play a part in how well a system works. To summarize, a healthy, well maintained bio-filter that is large enough for the size of the pond, will go a long way toward keeping water clear. However, filters are slow to react, and changes in fish load or food load can cause filters to become out of balance causing levels of nitrates and phosphates to rise to the point where algae can grow. Regular water changes help keep nitrate and phosphate levels in check.

Algae also needs light to survive. By shading a pond, algae will not survive. This may be done in several ways. Water plants that have foliage on the surface will work, however it will take 50% to 75%, shading to achieve this. If watching fish is your main goal this may not be the answer. Plants also help control algae because they are a direct competitor for the same food as algae. Some systems have filters that return into a "plant" pond before returning to the main pond. This may be an option. Another method is to construct a physical structure to cover the pond. Shading may also improve the colors of your fish by preventing sun fading. Shading by placing dyes in the water may work to eliminate algae but generally leave the water an unnatural color and may be harmful to fish. Even though algae may not be growing in your pond due to shade, don't forget that high levels of nitrates, etc. may still be present in your water. Regular water changes are important, even if there is no algae bloom.

Yet another way to deal with the algae problem is to just let it grow and then kill it. This can be accomplished in two ways. One is by the use of algaecides, algae-killing chemicals in the water. While this may be a solution there are several problems with algaecides. They may not be safe for fish and those that are may not be safe for koi. Also, algaecides are really just a temporary answer and don't really solve the problem. The other way to kill algae is by the use of an ultraviolet sterilizer light. These work by killing algae as they pass by the light, and are hooked to the filter system as the last stage. U.V. lights are a good permanent solution and also kill a lot of bacteria and parasites. However, they will have no effect on anchored or attached algae. They only kill what can pass in front of the light.

Temperature is a major variable in the growth of algae. While algae growth slows as the temperature drops, the activity of the bio-filter also slows down, which reduces its ability to handle waste material. At the same time, fish still eat and produce waste even in water temperatures in the fifties. These are times when water chemistry can get out of balance and produce algae blooms and other problems.

In nature, algae plays an important part in the water environment. It helps shade the fish from the sun and is a part of the natural food chain. Where clear water exists in nature it is due to plants shading the water and competing for food or spring fed waters-water changes! While algae may not be desirable in our ponds, it is a natural part of the water environment and to control it we must understand how it grows and what it needs.

FINAL NOTE
Algae produces oxygen during the daylight hours but reverses the process and consumes oxygen at night, thus reducing the oxygen level in the water. Fish found gasping early in the morning are a sign of the problem.