Pool Water: What are You REALLY Swimming In?


If you own your own pool, chances are you have probably already opened it for the summer and know the basics of pool maintenance regarding cleaning and filtration. But when it comes to truly keeping up pool water hygiene, it helps to know a little bit more to ensure the water you swim in isn’t doing your body and pool equipment more harm than good. Pools should always be tested regularly, as it is often the case that many people have no idea the kinds of bacteria and contaminants present in their pool water. For example, field studies looking at the different kinds of bacteria found in pool water discovered that upwards of 70% of public pools tested positive for human fecal matter. Of course, your own pool is going to have significantly lower levels of contaminants than pools that attract hundreds of swimmers per day, but it is no less important to keep an eye on what actually goes on in your pool water, and to know what to do to both prevent and correct potentially harmful levels of contaminants.

According to a brochure released by Siemens Water Technologies, the two most important factors in maintaining healthy pool water are chlorine and pH levels. Both are fairly easy to maintain and control, but there are several misconceptions surrounding the exact function and importance of each, and these misunderstandings could be inviting unwanted elements into your pool water. That is why this week’s topic is focused on the ins and outs of understanding chlorine and pH balance, just in time for the start of pool season.


Chlorine is absolutely crucial to ensuring the quality and cleanliness of your pool water, as it works to kill bacteria and microbes from people, animals, dead wildlife, and debris from around your yard. You would think chlorine would be the most straight-forward element of pool water maintenance, but many people caring for their own pools do not use it properly, and this can give rise to a whole host of problems regarding the quality of your pool water. Here are the top four mistakes people make with chlorine, and what to do instead:

  • Using liquid bleach. While bleach may be a convenient alternative and prove pretty effective in terms of bug- and bacteria-killing, it just doesn’t do the job as well as chlorine. Bleach will filter out faster than chlorine, and can cause more irritation to eyes and skin, as well. Your best bet is to stick to chlorine tablets, which are easy, affordable, just as effective in cleaning, and work much longer than bleach.
  • Adding chlorine during the day. Exposure to sunlight tends to dissipate chlorine, making it overall less effective. It is generally recommended to add chlorine at night, so that it has time to circulate throughout the entire pool before the sun rises. It is acceptable, too, to add chlorine to your pool early in the morning, before the sun is at its full intensity.
  • Not letting the chlorine circulate long enough. Good circulation is key to making sure your pool is as clean as possible. Think of it this way – when making chocolate milk, you can’t just squeeze in some chocolate syrup and expect it to mix on its own. If you don’t stir the chocolate well enough yourself, you end up with chocolate stuck on the sides and bottom of the glass in clumps. The same thing happens with chlorine. The better the circulation, the more evenly and thoroughly the chlorine will be distributed throughout the pool. You should count on running your pump for approximately one hour for every 10 degrees of temperature (on average, that is 8 to 9 hours a day in the summer).
  • Using too much chlorine. While we all want to make sure our pool water is as clean as can be, it really does not require much to do the trick. A little bit of chlorine goes a long, long way and it is much more important for the chlorine to be well-circulated than it is for there to be an abundance of it. The amount of chlorine you should be using differs depending on the size, shape, and depth of your pool. For a quick and easy reference guide, click here.

Keep in mind, as well, that it is definitely important to add fresh chlorine to your pool every day. It only takes days of neglect for your pool water to begin to take on a murky, green consistency, especially if you live in area where heavy rains in the summertime are prevalent.

pH Levels

Similar to how too much or too little chlorine can make you sick, so can too high or too low a pH level. We all learned about acids and bases in high school science class, and this is just one example where that knowledge proves useful in everyday life. A pH level of 0 is highly acidic, while a pH level of 14 indicates extreme alkalinity. A pH level of 7 is a neutral state, but most pool experts recommend a pH level somewhere between 7.0 and 7.6. Pool water that falls outside of this acceptable pH level range can cause damage to both you and your pool, and it is recommended you check pH levels at least once, even twice, per day.

If pool water is too acidic…

  • Swimmers’ eyes and noses start to burn and their skin feels dry and itchy. High acidity will also cause swimwear to fade faster.
  • Especially in Marbelite, plaster, or tiled pools, acidic pool water will begin to dissolve the surface, forming tiny groves ideal for algae and bacteria growth. High acidity will also cause metals – pool equipment, pipe fittings, pipe connections, ladders, etc. – to corrode. In addition to causing direct damage to these fixtures, metal corrosion will release sulphates onto the walls and floor of the pool, causing black and brown stains.
  • High acidity over-activates chlorine, causing it to dissolve and become lost to the atmosphere very quickly.

If pool water is too alkaline…

  • High alkalinity also causes irritation to swimmers’ eyes and skin.
  • The sides of the pool will begin to blacken at the water line due to calcification. The calcium carbonate will also plate out on the sand in the swimming pool filter, essentially turning to cement which causes the filter to lose its ability to function properly.
  • Pool water becomes visibly cloudy and murky.
  • A higher pH level minimizes the effectiveness of chlorine. Unlike in highly acidic water where the chlorine over-activates and dissolves, in high-alkaline water the chlorine is rendered virtually useless. Only about 20% of the chlorine in your pool is used when the water is at a pH level of 8.0, which means the vast majority of the chlorine (and the money you spend on it) goes completely to waste.

Keep in mind that the pH level of pool water will generally rise on its own, as it is nature’s tendency to balance standing water at a pH of 8.5. High alkalinity of pool water is easy to correct by (carefully!) adding small amounts of acid to the pool, the most commonly used acids being liquid hydrochloric acid (muriatic acid) and dry acid (sodium bisulphate).

To add acid to the pool…

  • Make sure the pump is running and that there are no swimmers in the pool.
  • Fill a bucket about 3/4 full of water from the pool.
  • Add a small amount of acid to the water. ALWAYS add acid to water, never the other way around!
  • Pour mixture slowly around the deep end of the pool.
  • Let pump circulate the acid throughout the pool for at least 4 hours.
  • Check pH levels again, aiming for a pH level of 7.2.

How do you keep your pool water clean and safe to swim in? Tell us about your maintenance routine in the comments section!

Happy swimming!

Kristen Turner

Featured blogger for Total Home Supply.

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