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What you need to know about Algae

What you need to know about Algae

We share our planet with zillions of different types of algae but there is only really one that pool owners need to worry about, the one commonly known as blue-green algae. The experts are now calling it cyanobacteria. That's because it is actually a cross between a plant and a bacteria and it is abundant everywhere. When it blows in to your nice warm pool on a sunny day it can multiply at an alarming rate and in less than a day you can go from having a perfectly clear water to water with a greeny-brown tint to something resembling a pond.

No one seems to know why, but you are most at risk after stormy weather. Some say the lightening gives them a growth spurt.

Chlorine will kill algae but sometimes the attack can be so bad that the algae is growing faster than the chlorine can kill it. It is a good idea to keep your pool dosed up with algicide.

There are lots of algicides and manufactures don't have to reveal on the label the full details so often it hard to know what is in there. Algicides fall in to three types. They are Copper based compounds, Quaternary Ammonium Compounds and Polymeric Quaternary Ammonium Compounds. The last two are quite a mouthful so the names are shortened to Quats and PolyQuats.

Copper is a very effective killer of algae. It is usually held in a complex of other chemiclas so that it can be released to kill algae. Quats are cheap but make the water foam and are short lived. PolyQuats are lots of Quats all joined together. They don't cause foaming as much as Quats. They slowly break down releasing Quats to kill the algae. By doing this they last longer and so make up the long-life algicides. One treatment with PolyQuat can last months.

Some algicides (like Fi-clor premium 5 long life algicide) use PolyQuats and copper. Some non-chlorine sanitisers like Nature2 and FROG also use copper so it is important not to use copper based algicides with them because it could lead to too high a copper content in the water and that can stain the walls etc.

It is important to remember that algicides only kill algae they dont dispose of the bodies. And the bodies are tiny, so tiny that they can go through a sand filter. To get the dead bodies out you must either use a shock dose of chlorine or some other oxidiser to break them up (see the Chlorine page for more on shocking) or use a clarifier to lump them altogether in to bits big enough for the filter to catch. It is best to do both.

From the cost point of view, it is better to kill an attack of algae with chlorine. So if you get a bad attack - shock dose your pool with Shock Chlorine (Calcium Hypochlorite). It will soon turn grey as the algae die. You must then filter it out using clarifiers to help. If you do use an algicide against an algae attack use a Quat not a PolyQuat.