This is a guide on tackling pond algae. If you're reading this, it probably means you have a fish pond or a water garden of some sort. To lets get to the meat of it shall we?
There are three main classifications that we can group these nuisance algae into. They are attached-erect algae, phytoplankton and filamentous algae.
And there are two reasons why these Pond Algae are taking over your pond. Light and nutrients. The type of nutrients we are concerned with are phosphates (po4) and nitrates (no3). Lets deal with nutrients first.
Both NO3 and PO4 are food sources for all plant life including pond algae. It seems logical to reduce them to a level where pond scum stops growing. To do that we need remove the primary sources of these nutrients. Which are organic material such as fish waste, fish food and anything that is slowly rotting in the pond. They will all be collected at the bottom of the pond in the form of sludge. This sludge, has got to go.
Get a rake and remove as much material from the bottom as you can. Siphon out all the sludge from the bottom while you're at it. This isn't feasible for much larger ponds. In such cases you can use auqtic plants to great effect. Floating and non-floating aquatic plants compete with pond scum for food. Floating plants have the added bonus of shading parts of the pond from sunlight. This is important as without light, they will die. Aquatics plants are a very natural way to combating pond algae and this method is highly recommended.
When dealing specifically with greenwater i have found uv sterilizers to be of great use. It breaks down the walls microscopic algae and causes great harm as the water passes through the uv light. You will however need a big enough unit as well as the proper water flow through the lighted area.
Barley straw can also be used with varying effectiveness against pond algae. And they are cheap so it is worth a shot. It is submerged into the pond and left there. Eventually, the barley will give out some chemicals that are harmful to most pond algae pests. This technique has seen plenty of use in Europe dating back hundreds of years ago.
