Swimming Pool Secret #8: All Those Algicides: Which is Best?

If you go into any pool store you'll find half a dozen or more different algaecides -- one for every problem, right?


In my opinion, there are only four GOOD pool algaecides:

  1. chlorine and some chlorine compounds,
  2. bromine and some bromine compounds
  3. 'poly-quat', and
  4. copper in various forms

So called 'linear quats' are the most widely sold swimming pool algaecides, and can be effective, but disappear quickly and tend to foam. In chlorinated or brominated pools, they also consume your sanitizer.

Virtually every packaged algaecide on the market contains one of these products, or a mixture of them.

You can also buy products of questionable valuable containing zinc or silver. You can even buy 'miraculous' pool magnets. But these latter products are more likely to cause mortal injury your wallet than your algae.

Oh! I should also mention: virtually all of the 'ionizers' simply add copper to the water. I have not seen any evidence that adding copper electrically is better than adding it chemically.

So what's best?

For quick kills of free floating, chlorine delivers -- unless you have stabilizer levels, above 60 or 70 ppm. Even then, if you add enough chlorine -- 10 ppm or more -- it will usually work just fine.

In this case, the chlorine compound, monochloramine, produced by using an ammonia source will work very quickly. Using either Yellow-Out (tm Coral Seas) or Mustard Master (tm Biolab) according to the label will produce effective levels. Aqua-ammonia, or ammonium sulfate will also do the trick -- but don't try it unless you understand the stoichiometry of the reactions involved. Using ammonia and chlorine together is tricky, and can be really dangerous! Even then, you don't want to use ammonia based treatments unless you have to do so: the monochloramine is much more irritating than the form chlorine ordinarily takes in a pool, and it will take several days of high added chlorine to convert the monochlorine back to more normal types.

United Chemical and others sell products containing sodium bromide which result in a free (unstabilized) bromine residual. And while bromine is probably not as good an algicide as lightly stabilized chlorine, it is a much better algicide than heavily stabilized chlorine! I've gotten very mixed feedback on these products; some people tend to swear by them, but others swear at them.

Unfortunately, using either ammonia or bromide containing products produce some pool 'gotchas' that can linger after the algae's gone. In particular, repetitive use of products containing ammonia can cause problems. For this reason, we recommend using them only if needed, and not routinely.

Poly quat -- poly[oxyethylene(dimethyliminio)ethylene(dimethyliminio) ethylene dichloride] -- is sold under multiple names. But if it says 'poly . . . ', it's polyquat. Unlike other algicides, it's nearly side effect free, even at very high doses. However, many people do become frustrated with its major unwanted effect: regular use tends to result in 'wallet-ectomies' (it's expensive!). And it's really better at preventing algae, than killing it. If you typically develop mustard algae in August, using low doses of polyquat beginning in late July may prevent the problem.

Copper can be added to your pool in a variety of ways, ranging from 'ionizers' to algicides to so-called 'chlorine-free' pool sanitizers. No matter how you add it, levels effective at killing algae are also effective at staining pools and blond hair. We use it -- but only on pools with rough looking plaster and exclusively dark-haired swimmers.

What's left? Quatenary ammonias! They're cheap, foamy, and might kill some algae. These are typically sold as highly diluted 'economy' algicides in gallon jugs, in blends with copper, and in a more concentrated form, for use in pools treated with PHMB (Baquacil, Softswim or PolyClear), since other algaecides are not compatible with PHMB based sanitizers.

So . . . what should you do?

The easiest thing is simply to avoid algae in the first place.

Want some algae preventing tips? Here are three:

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