Algaecides are available in many forms, shapes and makes. Liquids, tablets, powders, blocks with endless new products appearing each and every year.
Regardless of the appearance, algaecides work on the one principle, namely to destroy the algae. This is either accomplished by destroying the algae directly or by “suffocating” it.
Below is a brief summary of common algaecides:
Quat/Polyquat Algaecides
Quats consist of liquefied ammonium salts and are the cheapest form of algaecides available. The quats will cover the algae and lower the water tension. Lowering the tension around the algae cells, will literally split open the cells, thus destroying the algae. Quat algaecides are regarded as weak and applicable only with a low algae infestation. Quat algaecides are sold in concentrations of up to 20% active ingredient (quaternary ammonium salts), polyquat algaecides have concentrations up to 60%. The dosage varies, ranging from 2-4 ppm. Overdosing can lead to a soapy water surface and foam development.
Copper
Copper is probably the oldest method to rid algae from the aquarium. Plants, live bearers, snails, and invertebrates are all sensitive toward copper. Copper should also be avoided in marine and reef set-ups. Copper is a toxic metal and very poisonous (it disrupts the photosynthesis process) if used persistently. Copper can accumulate over time as it does not evaporate from the aquarium water.
Simazine
Simazine is the most common ingredient in commercially available algaecides. This chemical works by penetrating the organism and destroying the food producing (photosynthesis) cells. Simazine is a long lasting chemical and the frequent use of this substance is not recommended. Simazine will affect plants in the same way as it affects algae.
What Really Happens
All of these algaecides, will work in destroying the algae in theory and at least for a short term. In the long run in a practical environment things are quite different however. The negative effects of all 3 of these types of 
algaecides have a severe negative impact on the overall health of the aquarium as outlined above.
If you really feel the need to use an algaecide you should only consider it as a short term option at best.
The reasons why algaecides do not life up to their expectations on a long term basis are twofold.
Introducing algaecide into the aquarium will lead to the rapid destruction of algae (and live plants as well). At first glance the “cosmetic” improvement of the tank makes us feel successful. However, this rapid destruction also creates an increased amount of waste in the tank, the dead algae itself, which our biological filtration is now left to deal with. Not only have we introduced a completely unnatural substances to our tank, but we have also strained the overall health of our aquatic environment.
The final result of the algaecide use is nothing less then the beginning of new and often more severe algae growth due to the increased water pollution.
What we created is a viscous cycle, which can lead to significant expenses not to mention much frustration.
Excess nutrients are the cause of algae. Eliminating algae, does not solve the problem. In order to deal with algae successfully the environment must be controlled as not to allow unwanted algae growth.
Algae plays an important role in the aquatic environment by providing enzymes to a balanced aquatic system, as well as an alternative and supplemental source of nutrition for many species.
Water, light, and nutrients equal algae. There will always be some algae in the aquarium.
