How to deal with algae problems in your pond.

One of the biggest perennial problems for the pond keeper is algae, either in the form of green water, which can make your pond look like pea soup and make viewing the fish all but impossible, or alternatively in the shape of blanket weed, which as it's name suggests can form a tangling mass which chokes ornamental plants and can pose a risk to fish. There can be few more depressing sights than your much loved pond clogged with dirty green strands of blanket weed, or murky green with a bloom of green algae so thick that your fish are invisible if any more than an inch below the surface. Fortunately there are several easy methods available to help deal with these problems as well as some simple ideas to help prevent reoccurrence.

The main causes of blanket weed and green water algal blooms are usually a combination of two factors - too much light and heightened nutrient levels in the form of nitrate and phosphates. These tend to occur alongside each other in spring time when longer daylight hours & limited shade from plants combine with higher waste levels from decaying plant matter from last years pond plant growth & increasing waste production from more active fish as well as a lack of competition for available nutrients from higher plants in the pond,(lilies, oxygenators, marginals etc). Together these factors can mean that the algae can multiply unchecked and rapidly lead to problems. Dealing directly with the excess light issue can be difficult. Overhanging or nearby trees that may offer shade to the pond can also be a problem as falling leaves in autumn can contribute to the nutrient problems when they fall into the pond. Shade is best provided by floating plants in the form of lilies, but these need warmer conditions to start growth and give the recommended surface cover level of no more than 50% so the algae often gets a head start. Because of this it is best to use other methods to suppress early season algal growth and allow the other plants to out compete it for light and nutrients later.

Dealing with green water is generally straightforward. The most effective method is using a UV,(ultra violet) clarifier. These are relatively cheap and easy to install and when coupled with a suitably sized pump and filter all matched to your ponds volume are extremely efficient. They work by damaging the algae’s DNA preventing it reproducing and making it clump together so your filter can remove it far more efficiently. Do be aware that you will need to carry out more regular filter cleaning when dealing with a bloom as the filter may become clogged with all the algae it is removing. If you don’t want to use this method then flocculants which cause the algae to clump together can be an effective short term remedy.

One benefit of green water is that it often prevents blanket weed growth, so removing the green water can often encourage blanket weed! By far the best method of preventing both is efficient bio-filtration of your pond coupled with regular water changes and vigorous plant growth to reduce nitrate and phosphate levels and starve the algae. If however you still have problems with blanket weed then there are several methods available that can have beneficial impacts on restricting it’s growth. There are several barley straw based products on the market which are thought to prevent new algae growth so when older cells die new ones don’t grow to replace them leading to a steady die back if treatment is continued. There are also several electronic products available which claim to disrupt and stop algal growth through various methods, the exact science behind many of these is unclear, but many people have had great success through their use so while they may not be the cheapest method they can be worth a try if other methods have failed.

On the whole green water and blanket weed problems are best dealt with by a combination of measures - efficient and well maintained bio-filtration, regular partial water changes to lower nutrient levels, good plant growth to out-compete algae, physical removal of blanket weed where possible and use of some or all of the methods outlined above. It is best where possible to be pro-active rather than re-active and prevent the algae getting a foothold so have your anti-algae weapons at hand in springtime and you should have a clear and algae free pond for the summer.