Swimming pools – Algaecides – Sanitizers

Swimming pool

Algaecides – Sanitizers

In my last article I covered some basics on water treatment and how I go about clearing up the supply into your house. Recently I have been monitoring some customer’s backwash water from P.O.E. “Pre House Filters” and what I have seen is disturbing. I have stopped washing my teeth in anything but bottle water or beer. With municipal water filtration, there is a process of dropping the dirt in the water to the bottom of a tank. This is called flocculation and the chemical used is called Aluminum Sulfate. If there is no correct dosing, (too little or too much) then it will stay in suspension and end up in our homes.

Algaecides – Sanitizers

This is not only a problem here in Thailand but in many other parts of the world. Each day the water needs to be tested to set the correct amount of dosing so as the coagulant does its job. The process is also used in start up of pools, especially here as the water is full of IRON. When a pool is first filled, the water would look like it is clear. Then once the chlorine is added the water is oxidized and viola you get brown or green water. Then a liquid coagulant in the correct dose is used to drop the IRON and dirt to the bottom of the pool, to be vacuumed to waste the next day.

Depending on your water source, the water in your pool may be turning brown/green on a regular basis. This is due to the top up water being used after evaporation or vacuuming.


The top up water being full of IRON & some MAGNESIUM which reacts with the sanitizer that has oxidized the pool water. A vicious cycle that unfortunately can only be remedied by using a different water source. It is this oxidation that is needed for the killing of the baddies in your swimming water. I have already covered the basic of water balance & sanitation in previous issues. However I will cover briefly some other methods – Chlorine and its different types have been covered and you know I recommend Salt Chlorination as the safest and easiest way to have a low maintenance pool. Bromine, Algaecides,


Oxidizers and Ionizers are other methods of sanitization. Bromine is really only recommended for indoor pools spa’s as it is effected by sunlight very quickly. When bromine is in use, you would need to shock your pool on a regular basis with an oxidizer. Not enough space here to explain why!

Algaecides are used to control algae and are really only an aid in keeping your pool clean. Better suited to fish & plant ponds as chlorine is not able to be used in these areas. If you look after your pool correctly then algaecide is not needed. If over dosed in your pool, your hair can turn green. Oxidizers work with sanitizers to rid your pool and spa water of pollutants. By definition, sanitizers kill things like algae and bacteria but they work very slowly and inefficiently when trying to remove waste products such as sweat, skin oil, shampoos, soap and urine.

This is where you need separate oxidizers.

Oxidizers destroy these undesirables. They do their part by breaking down the contaminant’s structure, rendering them vulnerable. The sanitizers can then attack and kill the organisms. Some products, such as chlorine, act as both a sanitizer and an oxidizer. Bromine, on the other hand, does not oxidize very well and therefore needs the aid of a separate oxidizing chemical to properly clean your pool and spa water. The marriage of sanitizers and oxidizers is an almost foolproof method of keeping invaders out of your pool and spa water.


Ionization is a process where an electrical current is sent to sacrificial anodes placed in the pipe work inside the pump room. These anodes introduce metals such as COPPER and SILVER into the water to help kill undesirables. Ionizers are only an assistant and should be used in conjunction with a residual sanitizer. They are frown upon by the Health Dept. in Australia and they are being banned in shipping by the E.U.


Steve Johnson is the Managing Director of “WET” Water Engineered Technologies (Thailand) and offers a broad range of “Commercial & Domestic” water filtration solutions, potable water, plus swimming pool design, construction, equipment and consultation.


Steve can be contacted on # 08484 28317 or email info@poolsasean.com