Basic Pool Chemistry 101

and bomb it.

And every time someone swims, they leave behind body oils, hair, dead skin, shampoo, soap, everything we humans put on our bodies and slough off on a daily basis.

The only thing keeping those contaminants from turning your pool into a black lagoon is sanitizer, probably the most important pool chemical you’ll ever use.

And in order for the sanitizer to work, other water attributes must be balanced: pH, alkalinity, and calcium hardness.

Finally, you’ll add pool chemicals to treat algae, to clear your pool, and to prevent staining, if you have hard water.

All of these factors work together to create balanced pool chemistry so you can swim in peace, so knowing what to use and how is crucial.

Sanitizer Regardless of the type you use, sanitizer’s job is to keep the water, well, sanitized. This means free of bacteria, viruses, algae, and other nasty things that can grow in untreated pool water. You have a few sanitizers to choose from. Chlorine The most popular pool sanitizer due to its efficacy and low cost, chlorine sanitizes your pool by oxidizing contaminants. It enters molecules and destroys them from the inside out. Chlorine is effective at killing viruses, bacteria, and algae, and will also help prevent algae from growing in the first place. Chlorine comes in two forms:
  • Granules: You pour filters and pumps directly into your pool water, where they dissolve and are distributed by your pool’s filtration system. This isn’t a very effective method, though. It’s time-consuming, and there’s a chance the chlorine won’t be evenly distributed, leaving pockets of not-so-sanitized water around your pool, as well as pockets of super-chlorinated water, which can damage your pool liner.
  • Tablets: Available in 1-inch or 3-inch sizes, chlorine tablets can be added to a floating chlorine dispenser, directly into your pool’s skimmer basket, or to an automatic chlorinator.
Any of the methods for using chlorine tablets will provide more even distribution, but we highly recommend you use an automatic chlorinator for the best dispersion rate, to handle the tablets less often, and to save you time. ProTip: The ideal chlorine level in your pool water is 3 parts per million (ppm). Anything less than that, and your pool water isn’t really clean. Anything more than that, and you need to dilute the water a little or use a chlorine neutralizer to get the level down. When it comes to chlorine, there is such a thing as too much of a good thing. You’ll also find two types available: stabilized and unstabilized chlorine. Stabilized Chlorine If you have an outdoor pool, to prevent the sun from burning off the chlorine in the water, you need stabilized chlorine. It has cyanuric acid, also known as chlorine stabilizer or pool stabilizer, added to it. The cyanuric acid protects the chlorine so it stays in the water three to five times longer, which means it’s more effective at keeping the pool clean, and doesn’t need to be replaced as often. This saves you money and time. ProTip: If the chlorine you buy doesn’t specifically say “stabilized” on the label, check the active ingredient. If it’s Trichloro-S-Triazinetrione or simply Trichlor, it’s stabilized. Important: If too much cyanuric acid builds up in your water, it can reduce the chlorine’s effectiveness. If this happens, the only way to reduce the level is to dilute your pool water by removing some and replacing it with fresh water. Or, if there’s so much cyanuric acid that diluting the water won’t help, you may have to drain the pool altogether. Unstabilized Chlorine This type of chlorine is vulnerable to the sun’s ultraviolet rays. They’ll burn the chlorine out of the water, reducing its sanitizing ability. This means you’ll have to add more chlorine to your pool more often, which means you’ll have to spend more money. So why would you ever want to use unstabilized chlorine? Well, if you have an indoor pool, you don’t have to worry about the sun eating up the chlorine. It can also be used as pool shock, especially since you shock your pool at night (you do, don’t you?), so again, there’s no worry about the sun. ProTip: If the chlorine you buy doesn’t specifically say “unstabilized” on the label, check the active ingredient. If it’s Calcium Hypochlorite or simply Cal-Hypo, it’s unstabilized. This type of chlorine is most often available in granules rather than tablets. Add the Cyanuric Acid Yourself Rather than using stabilized chlorine and risking the level of cyanuric acid building up too much, you can use unstabilized chlorine and add cyanuric acid to the pool yourself. This gives you more control over the amount of cyanuric acid in your pool water. ProTip: The ideal cyanuric acid level in your pool water is 100 ppm or less. Chloramines During the oxidation process, chlorine dissipates and eventually becomes a waste product called chloramines. When you approach a pool and you smell that distinctive “pool smell,” it’s not the chlorine; it’s the chloramines. They’re also what sting your eyes and dry your skin when you swim. They’re also not the best thing to breathe in. To keep chloramines under control, you must add chlorine to your pool on a regular basis, according to how much it needs, which you’ll determine by testing your water. And if the chloramines get really bad, and your pool gets really stinky, you’ll need to shock it to get rid of them. The good thing is, you’ll be shocking your pool on a regular basis anyway (Right? Right!), so that will help manage chlorine and chloramine levels. Bromine The most popular alternative to chlorine, bromine works by ionizing contaminants. This means it breaks molecules’ chemical bonds and forces them apart, thereby destroying them. The benefit bromine has over chlorine is that as it works, it doesn’t break down quite as quickly, so it remains active longer. The downside is that as it breaks down, it creates waste products called bromamines. While not as nasty and smelly as chloramines, they still reduce bromine’s effectiveness. The solution is the same: shocking the pool. It’s also important to know that bromine tablets for your pool won’t be pure bromine. They’ll contain a small percentage of chlorine for an extra sanitizing boost. ProTip: The ideal bromine level in your pool water is 5 ppm, and never let the level drop below 3 ppm. Biguanide Does this sound like a medical substance? That’s because it is. Well, it was. Preservative-free polyhexamethylene biguanide, better known as PHMB, is also known simply as biguanide is a chlorine-free sanitizer. It was originally developed as a surgical disinfectant, and is similar to hydrogen peroxide. Biguanide works by forcing contaminants to bind together into water-insoluble clumps. This makes them easier for the filter to grab. The downside is it can cause the filter to clog frequently. So why would you use it?
  • It doesn’t produce chloramines.
  • It’s gentler on your skin, hair, and eyes.
  • It doesn’t degrade in sunlight.
  • It doesn’t turn blond hair green in the pool.
But it has its drawbacks too.
  • It’s more expensive than other sanitizers.
  • It’s not as effective as other sanitizers.
  • It loses its efficacy over time.
  • It can cloud your pool water.
Biguanide is sold under numerous brand names, the most popular—or at least, the best known—being Baquacil, which offers a complete line of pool chemicals designed to work with biguanide, from algaecide, to alkalinity increaser, to pH decreaser, and even test strips that measure biguanide levels. Be sure to fully research biguanide before you convert your pool from any other sanitizer to make sure you’re prepared for the different pool maintenance requirements. ProTip: The ideal biguanide level in your pool water is 30 ppm to 50 ppm. Never let it drop below 30 ppm, or you’re not getting any water sanitization at all. Minerals Have you ever looked at the label on a bottle of vitamins, and seen metals like iron and copper listed? That’s because they’re minerals, and are essential to our bodies’ health in small doses. Pool mineral systems use metals to sanitize water. Specifically, silver and copper. Silver is a known bactericide, and copper is sometimes used as an algaecide. When those metals come into contact with water, they release positively charged ions, which destroy negatively charged contaminants. Mineral sanitizer systems may also include borates and magnesium chloride as active ingredients, which have a few added benefits such as algae-fighting properties and skin soothers, respectively. It’s important to know that mineral systems aren’t complete sanitizer systems. They’re meant to supplement chlorine or other sanitizing pool chemicals, thereby reducing the need for as much of the other sanitizers. ProTip: When using a mineral sanitizer system, the ideal chlorine level in your pool water is 0.5 ppm. Now that you have the basics of sanitizers down, let’s look at some of the other facets of balanced pool chemistry, and the pool chemicals that will help you achieve them.