What Happens To Algaecide?

[macgd016]

I bit of a random thought but is algaecide solely an inhibitor or like Free Chlorine is it consumed/converted when it fights algae.

[waterbear]

I bit of a random thought but is algaecide solely an inhibitor or like Free Chlorine is it consumed/converted when it fights algae.

Depends on what type of algaecide you are talking about.

Quats are destroyed by chlorine

Polyquat also but more slowly. The long chain molecules break down into smaller ones that still retain some algaestatic properities.

both of these work by disrupting the cell membranes on the algae, making it easier for the chlorine to enter and kill it.

Copper and silver based ones eventually comes out of solution as stain, either on the pool, filter, or someones hair and nails!

Inorganic and organic ammonia treatments combine with chlorine to form monochloramine (and take high CYA levels out of the picture.) Monochloramine is destroyed by shocking and sunlight.

Sodium Bromide converts a chlorine pool into a bromine pool and is also destroyed by shocking and sunlight. It also takes high CYA levels out of the loop.

Borates tend to stay in the water and are only lost by backwashing and splash-out. IMHO, they are my perferred algaecide since they also have some pH buffering effect and make the water more "comfortable". The benefits of borates are especially useful with SWGs and biguanide pools (which need a higher level to be effective).

[chem geek]

The answer depends on the type of algaecide that is used.

Polymeric Quaternary Ammonium compounds aka "PolyQuat" with the most common being the ingredient "Poly{ oxyethylene (Dimethyliminio) Ethylene (Dimethyliminio) Ethylene Dichloride}" will slowly get broken down by chlorine and are also clarifiers so will consolidate particles and get caught in the filter where they will be removed through backwashing or cleaning of the filter. So they need a weekly maintenance dose to maintain their concentration. This algaecide will attach to algae cells, but it will not get consumed or used up by them, though will likely get filtered out.

Linear, non-polymeric Quaternary Ammonium compounds aka "linear quats" with ingredients such as "Dimethyl Benzyl Ammonium Chloride" break down even faster from chlorine so also need to be replenished weekly. These algaecides tend to foam. This algaecide will attach to algae cells, but it will not get consumed or used up by them, though will likely get filtered out.

Copper-based algaecides will generally not get consumed or used up in significant quantities. The copper level would only need to be maintained to make up for water dilution. Copper (and other metal ions such as silver) can stain pool surfaces if their concentration or the pH gets too high.

Sodium Bromide algaecides turn the pool into a bromine pool where the bromine will get consumed oxidizing algae. If the amount of product that is used is small, the bromine will eventually outgas, but if you add it regularly as with products such as No Mor Problems®, then you essentially turn your pool into a bromine pool.

Ammonium algaecides, such as those with ammonium chloride, will combine with chlorine to produce monochloramine which can kill algae. It will get consumed in doing so. Also, once you add chlorine again, the monochloramine will get oxidized by the chlorine to nitrogen gas.

Of course, chlorine alone can kill algae and prevent algae growth so that no algaecide should ever be necessary, but you need to maintain the appropriate Free Chlorine (FC) level relative to the Cyanuric Acid (CYA) level. See the Pool School for more details.

[macgd016]

Great thanks guys