What Is Total Alkalinity and Total Hardness?

It is important that your swimming pool maintains a stable chlorine level and the proper chemical balance. The balance of your pool consists of three components: pH, total alkalinity, and hardness. If your chlorine level is low, you add chlorine to the water. If your pH needs to be adjusted, you add an acid or a base.

Total Alkalinity

Total alkalinity is an important measure that, while having an effect on pH, is separate from pH. The total alkalinity of your pool is a measure of the amount of alkaline substances in the water. Alkaline substances can cause the pH of your pool’s water to change in an uncontrolled manner. When your total alkalinity is low, it makes the water aggressive and causes rapid fluctuations in the pH. When it is high, it causes cloudiness, lime precipitation, and makes the pH difficult to adjust.

To maintain the proper total alkalinity, it is important to follow the guideline figure for your daily or “shock” chlorination of 60-100 ppm (mg/l) and the guideline figure for your weekly chlorination and Halobrom of 90-125 ppm (mg/l). Total alkalinity can be reduced with sodium bisulphate and increased with sodium bicarbonate.

Total Hardness

The hardness of your water is a measure of the amount of lime dissolved in the water. Water with a calcium hardness of less than 100 ppm (mg/l) is described as soft water. Soft water can draw lime out of tile grouting and the concrete of cast pools, which can lead to disintegration.

Water with a calcium hardness above 300 ppm (mg/l) is described as hard water. Hard water can cause lime to be precipitated. Lime precipitation can lead to limescale forming on the pipes and walls of the pool, and within the mechanical equipment of the pool. The guideline figure for total hardness of the water is 100-300 ppm (mg/l).

The most common way to get larger amounts of dissolved calcium in your pool water is through chlorine. When you add chlorine to your pool water, you are not just adding chlorine, but also calcium, which is used to bind the chlorine. Total hardness can be reduced by dilution with fresh water and increased with the addition of calcium chloride.

Testing and Adjustment

Total Alkalinity: You should test the total alkalinity of your pool once a week. Dip a test strip about 18 inches below the surface of the water, following the manufacturer’s instructions, then remove. Compare the test result color against the test kit guide to determine the total alkalinity level. Concrete and concrete-related pools require a total alkalinity level of 80 to 120 parts per million (ppm). Levels of 125 to 170 ppm are recommended for vinyl, painted, and fiberglass pools.

Measure out your preferred choice of chemical for lowering the total alkalinity (sodium bisulphate or muriatic acid). Remember to read the product instructions carefully before you treat your pool water, as different manufacturers suggest different procedures or amounts of product to be used. Typically, treatment consists of 24 ounces of sodium bisulfate or 20 fluid ounces of muriatic acid per 10,000 gallons of water, which is enough to lower the total alkalinity by 10 ppm. Broadcast the sodium bisulphate or muriatic acid in the deep end of the pool, or the end where the water return distributes water if your pool does not have a depth change. You want to be close to, but not actually touching, the water. Make sure to add your alkalinity decreaser directly in front of the water return, as that helps distribute the chemical quickly and evenly.

Retest the total alkalinity again in six hours. If the reading was too high the first time, it may have been inaccurate due to levels above the maximum reading. Re-treat the water as needed, making sure to test the water and continue treating every six hours if necessary.

Total Hardness: To test your pool water’s hardness, dip a test strip 18 inches below the water surface or as directed by the test strip manufacturer. Remove the strip and wait for the color to change and indicate the level of hardness. Ideal levels of water hardness rest between 200 and 400 ppm.

To adjust the hardness of the water, drain a portion of your pool. In areas with very hard water, it is common to drain your pool once or twice a year, but water hardness can vary both in and between regions, so the best bet is to contact a pool professional to see what works best for your area. Fill a portion of the pool with softened water or order pool water that has been treated. Using commercially purchased pool water that has already been treated and balanced gives you a head start on fixing any chemistry issues and is as easy as running a hose from the truck to your pool.

Add a commercial hardness reducer to soften your water to the ideal levels. Follow the product instructions, which usually require that you measure and pour the recommended amount of hardness reducer into a clean plastic bucket. Broadcast the treatment slowly as you walk around your pool. If it isn’t already running, turn on your pool pump and keep it running for the next 24 hours. Increase the pH to 7.8 to 8.2 for five days after treatment, adding borax or soda ash. Borax is preferable as soda ash tends to raise the total alkalinity and pH. Wait seven days and test the water hardness again. If the water hardness is still high after those seven days, retreat the pool.

If you want to avoid all of these hassles and ensure the water in your pool or hot tub stays balanced, consider pHin. It constantly monitors your water and tells your smartphone what you need to do to keep the water in your pool and hot tub healthy. Use it with your own chemicals for flexibility or get our single-dose, pre-measured chemicals delivered to your door. If you need someone to service your equipment, Pool Service on Demand connects you to local, qualified pool techs.


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