Water Chemistry 101

Maintaining proper water chemistry levels can be frustrating at times, but with an understanding of the basic science involved, you'll find it's not so hard after all!

1) Total Alkalinity

Total Alkalinity is a measurement of waters ability to neutralize an acid. Considering that pH (up next) is a measurement of the acidity of your water, we can see how these two readings are strongly related!

When Total Alkalinity is balanced properly (100-120 PPM), your pool will be very resistant to pH influences from the outside world (rain water, debris, swimmers, and etc).

Alkalinity too low: When Total Alkalinity is too low, your pH can jump all over the place. This is sometimes called “pH bounce”, and it can make water balancing impossible!

Alkalinity too high: When Alkalinity is too high, your pH will drift up to drastically high levels – and stay there! High TA will make your pH levels very stubborn and hard to control.

Because of the direct relationship to pH, Total Alkalinity is always the first element you should test (and adjust!) when correcting your pool water.

Recommended Range: 100-120

Increase: To increase Total Alkalinity, sodium bicarbonate (referred to simply as Alkalinity Increaser) should be added to your pool.

Decrease: To decrease Total Alkalinity, we need to add an acid to our pool. Or put another way…we want to decrease our pH! You guessed it, to decrease Total Alkalinity, we use a pH decreaser!

2) pH Balance

pH is a measurement of your waters acidity. The range goes from 0 (very acidic) to 14 (very alkaline, or basic). We want to go right down the middle with pH, and shoot for a range of 7.2-7.6. Fun fact: the human eye has a pH range of 7.0 to 7.3. It’s no surprise that a pool with this pH would be nice and comfortable!

pH too high: If pH is too high, your water is too basic. This can result in scaling, calcium build up, dull water, damage to filtration equipment, burning nose and eyes, and last but not least: a non-sanitary pool! Yup, when pH is too high, chlorine becomes far less effective at doing it’s job. How strong is the pH/chlorine relationship? Very! Check out the following graph:

As you can see, chlorine effectiveness drops sharply as pH rises. At a pH level of 8, chlorine is only about 20% effective. If it’s your goal to start an algae farm in your backyard, letting your pH get out of hand is a great way to start!

pH too low: When pH is too low, on the other hand, your water is too acidic. Again, swimmers will experience eye and nose discomfort. In addition, anything metallic that is in contact with your water (such as stairs and rails) will become corroded and etched. And the final “gotcha” to low pH: your chlorine will evaporate much, much faster. It makes good financial sense to keep your pH in check!

Recommended Range: 7.2-7.6

• Sodium Hypochlorite pools should Muriatic Acid or C02 to control pH
• Calcium Hypochlorite pools should use Muriatic Acid to control pH
• Gas Chlorine pools should use Sodium Carbonate to control pH
• Trichlor pools should use Sodium Carbonate to control pH
• Dichlor pools should use Sodium Carbonate to control pH
• Bromine pools should use Sodium Carbonate or C02 to control pH

3) Calcium Hardness

Calcium Hardness refers to the amount of calcium dissolved in your water. You’ve probably heard the terms “hard water” (too much calcium) and “soft water” (not enough calcium) in regards to tap water. Well, it’s no different for pools! We want to shoot for a calcium value in the neighborhood of 200-400PPM.

An important point to understand with calcium is thus: your water wants to be at a proper calcium level. Water tends to seek a balance, and if calcium is out of whack, it will naturally attempt to make corrections.

Calcium too low: If your calcium level is too low, your water will leach calcium from its containing vessel; your pool liner! This can lead to irreversible etching damage. Low calcium water is very corrosive.

Calcium too high: If your calcium level is too high, your water will deposit calcium on anything it touches! This can lead to unsightly stains, a feeling of “sticky skin”, and even deposits in your plumbing and heater. In addition, high calcium water can appear cloudy.

Recommended Range: 200-400PPM

Increase: To increase calcium, simply add calcium to your water. Decrease: The easiest method to decrease calcium is by diluting your pool water (draining and adding fresh water). The obvious catch here is that if your source water has high calcium, so too will your pool. If this is the case, check your local Yellow Pages for pool water delivery.

4) Free Available Chlorine

The three measurements of chlorine can be confusing for new pool owners (or even new commercial operators!), but it’s actually pretty simple once you get the concept.

Let’s say we fill a pool with 100% pure, clean water. To this water, we add enough chlorine to bring our levels up to 3PPM. At that point, 100% of our chlorine is free, available chlorine. This is obviously ideal, and no further action would be required of us. Life is not a bowl of cherries, however! At some point, a mess is going to be introduced into our pool. Sunscreen, urine, grass clippings, whatever! When that happens, our chlorine is going to latch on to the contaminating molecules, disinfect them…and unfortunately create “chloramines” as a by-product of the reaction. The result? We now have two types of chlorine in the pool. Good stuff (free, available chlorine) and not so good stuff (chloramines, AKA combined chlorine). Add the two types of chlorine together and what do you get? Total chlorine!

When we test, we are primarily concerned with modifying our free chlorine to be within the required range. Occasionally, however, our total chlorine is going to exceed our free chlorine by a certain threshold. When that happens, it’s time to shock!

The Different Chlorine Forms Explained:

Sodium Hypochlorite: Sodium Hypochlorite is a liquid and contains 10-12% available chlorine (AC). Household bleach contains 5% Sodium Hypo, and so can technically be used as a (relatively weak) form of chlorine. Due to it’s liquid form, sodium hypo is generally dispensed via an automated chemical pump system. Commercial pool operators love the convenience and consistency offered by sodium hypochlorite.

Side note: If you have a salt pool, you technically use sodium hypochlorite since this is how your cell breaks down salt.

Lithium Hypochlorite: Lithium Hypochlorite is granular Chlorine with a 35% AC. Because lithium dissolves very quickly, it’s great for shocking vinyl and fiberglass pools. In addition, lithium hypochlorite contains no calcium. This makes it a great option for those with high calcium water!

Calcium Hypochlorite: The most popular of the chlorines, calcium hypochlorite has an AC of 40-78%. It is commonly sold as granular, but is also available in tablet form. Great for both shocking and general sanitization duties.

Dichlor: These are “stabilized” Chlorines making them perfect for outdoor pools. Their AC level is usually around 80-90% and introduced to the water thru chemical feeders or skimmers. Because of their high AC level the granular form it commonly used to treat pool problems due to algae or a chlorine demand.

Recommended Chlorine Range:

Residential: 1-3PPM , Commercial: 2-4PPM , Hot Tub & Spa: 3-5PPM

To Increase Chlorine: Simply add your chlorine of choice.

To Decrease Chlorine: To decrease chlorine, you just…wait! It’ll go down all on its own. In extreme cases (you just shocked your pool, but forgot about the pool party this evening), chlorine can be decreased with Sodium Thiosulfate,