Copper sulfate in pool

[markjimenex]

I am a new owner of a swimming pool. Upon turnover of my new pool, I was instructed by the contractor to buy certain kilos of copper sulfate to be poured into the water and as part of the procedure in chemical treatment. Can you give me an idea as to what it does? is it really necessary to have this chemical?

[chem geek]

Copper ions (either from copper sulfate or from an copper ionizer) are a powerful algaecide that will kill existing algae and will prevent algae growth. However, copper at such levels can stain plaster if the pH rises and can have blond hair get a green tint. It is only one of several ways to control algae.

Another approach without the side effects of staining is to use a weekly maintenance dose of PolyQuat 60 algaecide. Yet another approach is to use a phosphate remover. All of these approaches cost extra money.

An approach that does not cost as much is simply to maintain a sufficiently high active chlorine level in the pool to prevent algae growth. The active chlorine level is proportional to the ratio of Free Chlorine (FC) to Cyanuric Acid (CYA). In a manually dosed pool, if you keep the FC at least at 7.5% of the CYA level, then you can prevent green algae growth. In a saltwater chlorine generator (SWG) pool, the FC should be at least 5% of the CYA level.

In order to prevent the buildup of CYA in the water, you want to avoid using only stabilized chlorine (Trichlor or Dichlor). The following are chemical facts:

For every 10 ppm Free Chlorine (FC) added by Trichlor, it also increases Cyanuric Acid (CYA) by 6 ppm.
For every 10 ppm FC added by Dichlor, it also increases CYA by 9 ppm.
For ever 10 ppm FC added by Cal-Hypo, it also increases Calcium Hardness (CH) by 7 ppm.

You can use either chlorinating liquid or 6% unscented bleach (e.g. Clorox Regular) since that will not add to CYA nor CH. However, it must be added every day or perhaps every other day unless you have a pool cover opaque to UV from the sun in which case you can probably add chlorine twice a week (in the summer; now, with cold temps, chlorine lasts a long time). This is why some people just use Trichlor in a floating feeder or inline chlorinator since it's slow-dissolving and so convenient, but you need to use a supplemental algaecide to prevent algae growth in that case.

You can see a chlorine/CYA chart and also learn much more about how to maintain your pool at the Pool School at Trouble Free Pool.

Richard