Swimming Pool Blog

Pool Chemical Myths & Misconceptions

Pool Chemical Myths
by Mark Garcia April 15, 2015

Pool chemistry is complicated. There are so many variables to consider, when trying to simultaneously keep balanced and sanitary water, while protecting pool surfaces and swimmers.

That is why myths are common around pool chemical use, or pool chemistry in general. What appears as truth can be false, because as with so many things, Cause doesn't necessarily equal Correlation!

Today's post is a curated collection of myths surrounding pool chemistry or pool chemical use. You've probably heard of some of these before, and some may challenge your belief system.


1. A strong chlorine smell is a good way to know the pool is sanitized.

If a pool smells strongly of chlorine - what you smell is combined chlorine, or chloramines. Free, active chlorine has no odor when in the water, but when it combines with nitrogen or ammonia, it becomes a foul smelling irritant. To remove chloramines, and a strong chlorine odor, it is necessary to shock the pool, to a level 10x greater than the level of chloramines, to break apart the combinations.

2. Chlorine makes the eyes red.

Like smelling a strong chlorine smell, red eyes can be an indication that the pool needs to be shocked, to remove chloramines in the water. Eye redness can also occur from a pool pH level that is significantly higher or lower than the eye pH, which is generally around 7.3. Thirdly, swimming underwater with eyes open for an extended period flushes the eye of tears, resulting in a "dry eye".

3. It's necessary to shock the pool every week.

Shocking the pool is only necessary for 3 reasons, the first of which is to remove chloramines, as described in myth #1. Second reason is to destroy visible algae, and the third reason is to oxidize the water, or kill any pathogens that have managed to escape normal, everyday chlorination. For most people, this works out to once a month being a good interval for shocking, although some low-use pools can go longer.

4. Test strips are just as accurate as test kits.

Not true! Test strips are very convenient and quick to use for pool water testing, but the results can be vastly different when tested side by side with a liquid drop style test kit. Readings can vary by 20% or more, resulting in inaccurate balancing from adding too little or too much adjustment chemicals. Test kits are OK for a quick test for chlorine or pH, but your pool water is best tested every week or so with a more accurate test kit, like the Taylor K-2005.

5. All pool chemicals are the same.

A long time ago, 30 years or more - this would have been true, but today chemists have fine tuned pool chemicals to perform better and have less byproducts or unintended reactions. Chlorine in particular can be made more cheaply with poor raw materials or inferior heating, cooling and drying equipment. Water balance adjustment chemicals are not as commonly altered, but can be packaged in lower concentrations or contain impurities.

6. Green hair is caused by too much chlorine.

Green hair is caused by copper in the water. Dissolved copper can come from heavy use of copper algaecide or from copper pipes or heat exchangers. It will rinse out of the hair with a quick shampoo, but if allowed to dry onto the hair, copper will add a tinge of green to any hair color, but it only becomes noticeable on swimmers with blonde hair.

7. Dogs or Ducks in the pool won't affect the pool chemistry.

I can tell you from experience, that regular use of the pool by dogs, or regular visits from ducks or other water fowl can foul your pool water. pH and alkalinity will rise, and all sorts of invisible bacteria enters the pool. Excessively hairy dogs can also clog a pump basket with shedding fur. Ducks also bring in phosphates and dirt, and like to use the pool as a toilet.

8. Chlorine & Cyanuric acid are components of water balance.

Technically No, although when speaking of water balance, it's common to group these two to the real components of water balance, which is pH, Alkalinity, Hardness and water temperature. A pool that is in balance will be one that has no propensity for scaling. To really balance your pool water, calculate the Saturation Index, which is easy to do using an online calculator, like this one by King Technology.

9. Cyanuric Acid works best at 50-100 ppm

Way too high. New information in the last few years has surfaced, regarding the suppressive effect of cyanuric acid (aka conditioner or stabilizer) on free chlorine. One of the ways that cyanuric acid protects chlorine from the sun is to limit its movement or activity. This also hampers it's ability to sanitize. At extremely high levels approaching 100 ppm, a chlorine-lock phenomenon can occur, where it becomes difficult to build a chlorine residual. Protect your chlorine from the sun, but do it with much less cyanuric acid; maintain the residual in the 20-30 ppm range.

10. The ideal pH level is 7.5.

I think that this one came about because we often hear that the pH range of 7.2 - 7.8 is appropriate, and 7.5 is exactly in the middle of the range. However, 7.5 is high by many pool operator's standards. Chlorine is much more active at a level of 7.2 - 7.4, and is still above the 7.0 mark, below which the water becomes acidic and may become aggressive towards pool surfaces and equipment. If it seems like a small movement, keep in mind that pH is a logarithmic scale, and each 1/10 movement in either direction is an increase or decrease of 10x.

11. It's OK to swallow pool water, if it's chlorinated.

Normal levels of chlorine (1-3 ppm) won't cause any problem if pool water is swallowed. But it's not the chlorine we are concerned with, it's the lack thereof - your pool water at any given time is never 100% sanitized. There are always pathogens and contaminants in the water that have yet to be eliminated, especially surrounding swimmers, who may ingest their own body waste, or that of others, if they swallow pool water. Keep your mouth closed while swimming.

12. It's OK to test your pool water monthly.

That may be OK for cyanuric acid levels, and maybe for calcium hardness levels, but pH and alkalinity drift more rapidly than that, and should be tested at least weekly, if not every few days. If you are in the habit of taking a water sample to the pool store every 4-6 weeks, you could be damaging your pool surfaces or creating unhealthy water by not testing and adjusting more frequently.

13. Filtration has nothing to do with water balance and sanitation.

Filtration and circulation does have a profound effect on water balance and sanitation. Keeping the water moving avoids pockets of dissolved solids or pH fluctuation. A good filter can reduce the chlorine demand, by removing small particles from the pool, which reduces the amount of work required of the sanitizer. If you don't believe me, cut back your filtration time to 8 hours per day, and watch your levels closely.

14. Clean and clear water is a good sign that the water is healthy.

It is a good sign, but not necessarily accurate. Pool water can be clean and clear but whacked on pH, alkalinity and hardness, or low on chlorine. Bacteria and viruses are invisible, and just because you can't see them doesn't mean they're not present in the pool. Alternatively, a pool that is cloudy or hazy, or even green - does not mean that the pool is unhealthy to swim in, but can still be sanitary while turbid.

15. Pool salt systems are a chlorine-free alternative.

False. Salt systems create chlorine. They are an alternative to chlorine tablets or other forms of packaged chlorine, but a pool salt system is a chlorinator. This myth may come from the idea that the ocean's saltiness is what keeps the water clean. Some people think that all you need to do is pour salt in a pool and you can go chlorine-free. Add salt without a salt cell, or a small electrolysis machine, and all you have is salty water.

I hope you enjoyed this look at some common misconceptions around pool chemistry. Here's one more, I'll be you know this one - there's no chemical that changes the color of the pool water in the presence of urine. But, you can continue to promote that myth if you want - anything to convince kids not to pee in the pool - which is bad for water balance, and creates chloramines.


Thanks for Reading!
Mark Garcia