Before you use any of the following information to adjust your swimming pool and/or spa chemistry, please refer to the safety information toward the bottom of this page.
Maintaining the proper water chemistry levels in your pool involves four major processes:
- Balancing your water (Water Balancing)
- Maintaining proper pH levels
- Maintaining proper Total Alkalinity
- Maintaining proper Calcium Hardness
There is also a fifth process, which involves the use of something know as the Saturation Index (SI), which can sometimes help you in achieving the perfect swimming environment.
The following list details the proper water chemistry levels for optimal swimming pool functionality and comfort:
- pH: 7.4 – 7.6
- Chlorine: 1.0 – 3.0 ppm
- Total Alkalinity: 80 – 140 ppm
- Calcium Hardness: 200 – 400
- Cyanuric Acid: 25 – 50 ppm
- Total Dissolved Solids: 500 – 5000 ppm
Water balancing is not a complicated exercise. It is simply the relationship between different chemical parameters. Your water is constantly changing, year round. Everything from weather to oils, to dirt and cosmetics, affect you water balance. You will probably not change the water in your pool for many years. Continuous filtration and disinfecting removes contaminants which keep the water enjoyable, but it does not balance your water chemistry. A pool that is balanced has proper levels of pH, Total Alkalinity, and Calcium Hardness. It can also be defined as water that is neither corrosive nor scaling. This concept is derived from the fact that water will dissolve and hold minerals until it becomes saturated and cannot hold any more water in solution.
When water is considerably less than saturated, it is said to be in a corrosive or aggressive condition. When water is over-saturated and can no longer hold the minerals in solution, it is in a scaling condition. Balanced water is that which is neither over nor under-saturated. The cliché that “water seeks its own level” certainly applies here. Water that is under-saturated will attempt to saturate itself by dissolving everything in contact with it in order to build up its content. Water which is over-saturated, will attempt to throw off some of its content by precipitating minerals out of solution in the form of scale. How do we know when our water is over or under-saturated? We use a good test kit (with fresh testing reagents) to measure the chemical parameters of pH, alkalinity, and calcium hardness.
pH is a measure of how acidic or basic the water is. pH is a logarithmic scale from 0-14, with 7 being neutral. pH values below 7 are defined as being acidic; while levels above 7 are said to be basic (or alkaline). Everything that enters your pool has a pH value. For instance, acid rain is rainfall with a very low pH. Then there’s the human eye with a pH value of 7.35, which is just slightly basic. This is, coincidentally, in range with proper pH levels for your pool. To have pH in balance we adjust the water with additions of pH increasers (bases) or pH de-creasers (acids) to achieve the range of 7.2 – 7.8. If your testing (which you should do daily) of the water indicates a pH value below 7.2, the water is in a corrosive (acidic) condition and you will need to add a base to bring the pH into a more basic range to prevent corrosion. Conversely, if the pH is above 7.8, we are in a scaling (basic) condition and must add an acid to bring down the pH to prevent the formation of scale.
A close cousin of pH, the level of alkalinity in the water is a measurement of all carbonates, bicarbonates, hydroxides, and other alkaline substances found in the pool water. pH is alkaline dependent: that is, alkalinity is defined as the ability of the water to resist changes in pH. Also known as the buffering capacity of the water, alkalinity keeps the pH from bouncing all over the place.
Low alkalinity is raised by the addition of a base (similar to pH), and sodium bicarbonate is commonly used. High levels of alkalinity are lowered by the addition of an acid (similar to pH). Experts recommend pooling the acid in a small area of low current for a greater effect on alkalinity. That is, adding an acid will lower both pH and alkalinity. Walking the acid around the pool in a highly distributed manner is said to have a greater effect lowering the pH than the alkalinity. Pooling the acid has the opposite effect. A very important component of water balance, alkalinity should be maintained in the 80-120ppm range for gunite and concrete pools and 100-140ppm for painted, vinyl, and fiberglass pools. Levels should be tested weekly.
When we speak of scale, we are talking about calcium carbonate that has come out of solution and deposited itself on surfaces. It is a combination of carbonate ions, a part of total alkalinity and calcium, and a part of the Calcium Hardness level. The test for Calcium Hardness is a measure of how hard or soft the water is when it’s tested. Hard water can have high levels of calcium and magnesium. If these levels are too high, the water becomes saturated and will throw off excess particles out of solution that then seek to deposit on almost any surface inside the pool. This is calcium carbonate scale: a “white-ish,” crystallized rough spot. If the levels are too low, the water is under-saturated, and the water will become aggressive as it attempts to obtain the calcium it needs. Such “soft-water” will actually corrode surfaces inside the pool which contain calcium and other minerals to maintain its hardness demand. If your Calcium Hardness levels are too high you can use TSP to lower the levels. This can also be accomplished by dilution (draining old water and adding water to the pool that has lower calcium hardness content). Levels which are too low, require the addition of calcium chloride. Recommended range for calcium hardness is 200-400ppm. Calcium Hardness levels should be tested monthly.
The Saturation Index
Also called the Langelier Index, this chemical equation (or formula) is used to diagnose the water balance in the pool. The formula is:SI = pH + TF + CF + AF – 12.1
To calculate the Saturation Index, test the water for pH, temperature, calcium hardness, and total alkalinity. Refer to a chart for assigned values for your temperature, hardness, and alkalinity readings, then add these to your pH value. Subtract 12.1, which is the constant value assigned to Total Dissolved Solids and a resultant number will be produced. A result between -0.3 and +0.5 is said to indicate balanced water. Results outside of these parameters require adjustment to one or more chemical components in you pool water to achieve balance.
Please note that the use of the SI formula doesn’t necessarily guarantee anything; however, some readings for pH, calcium, and alkalinity which, if taken individually, might be considered to be well beyond recommended levels. But you can use those test readings in combination with the formula to help achieve “balanced water” in your pool. The SI formula can thus be used to help pinpoint potential water balance problems.
Safety Information | Legal Disclaimer
Please note that any information associated with pool and spa chemistry that we provide via our web site is provided as a service to our customers to allow you to adjust your chemistry yourself. That said, if you do adjust your chemistry yourself, we have to warn you that you do so at your own risk. Swimming pool and spa chemicals can be dangerous to your health and even harmful to life and and/or property if not handled with appropriate care, and require special handling and storage methods. The Ultimate in Pool Care will not be held responsible for any injuries to your health, life, and/or property associated with the use of information in the tables included in this document. Please refer to the special SAFETY CAUTION that follows for more information.
SAFETY CAUTION: Swimming pool and spa chemicals can be dangerous to your health and require special handling and storage methods. Before using the information provided in this document, please ensure you review Safe Storage and Handling of Swimming Pool Chemicals provided by the United States Environmental Protection Agency (U.S. EPA). This document can be found at https://www.epa.gov/sites/production/files/2013-11/documents/spalert.pdf.