Controlling Algae In The Pond
Algae is present in every pond, which isn’t a bad thing. In fact a moderate amount algae is beneficial for the overall balance of a pond. Algae only can become a problem when it grows out of control. New ponds and even established ponds during the spring often provide ideal conditions for excessive algae growth.
Types of Algae:
There are 2 main types of algae common in most ponds:
- SUSPENDED ALGAE which causes green murky water. Sometimes resembling pea soup in extreme cases, making it difficult to see fish that are just a few inches below the surface of the water.
- FILAMENTOUS or STRING ALGAE, also known as blanketweed. This type of algae forms either dense mats or long threads around plants, rocks and other objects in the pond. It is also creates unsightly mats on waterfall and streams.
Causes of Algae:
- SUNLIGHT – inadequate plant coverage at the pond’s surface allows too much light into the pond enables algae to flourish.
- DISSOLVED NUTRIENTS – Fish waste, decaying leaves, uneaten food (ammonia, nitrates, phosphates), minerals from tap water etc. provide food for excessive algae growth.
- WARM WATER – often caused by shallow ponds, inadequate plant cover, poor circulation.
Recommendations to Control Algae in Ponds:
- Do not drain the pond and completely change the water. Although the pond will look good for a few days or even a couple weeks, this will only upset any balance in the pond and add a fresh supply of dissolved minerals to feed the algae and cause the process to start over again. Plus, this is usually very stressful and possible dangerous for your fish.
- Try to achieve a natural biological balance in the pond. Adding the right combination of plant material (oxygenating plants, water lilies & floating plants) will result in clear water without the need for chemicals which often only temporarily clear the water.
- Cover 50-60% of the pond’s surface with plants. The best are floating plants like water hyacinth, water lettuce, duckweed or azolla because they multiply very quickly. Water lilies or lotus are also very good because they provide shade. also submerged plants such as hornwort work great as well. This should provide enough shade to keep the water cool as well as block enough sunlight to keep algae growth to a minimum.
- Use one bunch of oxygenating plants for every 2-3 square feet of surface area. These plants compete with algae by absorbing excess dissolved nutrients and also provide O2. Plants such as hornwort, water thyme, pond weed & parrot feather are ideal.
- Keep fish numbers at a reasonable level. A pond stocked heavily with fish is more likely to have significant algae growth. Waste from fish is converted in to nitrates, which contribute greatly to the growth of algae. If you have more than a few fish in the pond, a biological filter and/or ‘bog filter’ may be necessary to achieve satisfactory results.
Products To Control Algae in Ponds
Barley Straw Pellets can be used to naturally control algae in the pond. Add it early in the spring because it takes a few weeks to begin to work. Sometimes string algae can get out of control very early in the spring or suddenly during very hot spells of weather. Sometimes you want to get a handle on it quickly so when all else fails, Pond Balance, a product from Interpet, works wonderfully. It is not an algaecide, so it won’t harm any other plants (or even free floating algae for that matter), it works specifically on string algae. Add it in the spring and periodically through the summer. A few weeks after the initial treatments, the string algae will fall right off the rocks, liner or whatever it is growing on. Clarity Max Plus is another product that works very well in just a few treatments. D-Solv also works great as a spot treatment for waterfalls. Recently, D-Solv9 a concentrated liquid, has become one of the most popular algae treatment because it works on both string algae and green water.
Suspended algae (pea soup green water) can sometimes also grow out of control no matter what you do. First see our info sheet GREEN WATER INFO for more information about controlling suspended algae, then consider installing an Ultraviolet Clarifier.