Swimming Pool Chemistry: The Best Chemicals To Use In Your Pool

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Keeping a swimming pool clear, clean, and safe is harder than it first seems. After all, there is a reason that stagnant water quickly becomes disgusting and unsafe to drink or play in. Standing water is prone to attracting algae, bacteria, and grime that transforms it into a murky pond in no time. However, the chemicals that prevent these agents from taking over standing water are usually also poisonous in their own right! Finding the right balance between nasty stagnant water and a toxic chemical bath requires some careful chemistry. If you have a pool, read on to learn from RS Pool Patrol about how to keep your chemicals in check for a safe, clear, beautiful swimming area.

Free Chlorine

The most important aspect of keeping your pool in check is the free chlorine level. Chlorine is the most basic pool chemical that every pool needs, and it needs to be monitored carefully. Too much free chlorine can make your pool water irritating to sensitive areas like the eyes. Too little, and algae will quickly start to bloom. If your chlorine level drops to zero or your pool starts to grow algae, your pool water is unsafe.

Make sure to check your chlorine levels every day and adjust accordingly. Free chlorine is used up from exposure to sunlight as well as breaking down the organic matter it is designed to combat, so your pool will not stay adequately chlorinated for long. Depending on how often you use your pool, your chlorine may be used up very quickly.

Combined Chlorine

The next chemical level to keep track of is the combined chlorine level. Combined chlorine is chlorine that is in the process of reacting chemically with organic matter to neutralize it. A low level of combined chlorine is expected, but if it reaches over 0.5 parts per million, you should do a complete cleaning to eliminate the contaminant.

Combined chlorine is the chemical that is responsible for the smell of chlorine that comes from a pool. When the pool is free of organic matter, the water will smell relatively neutral. A strong chemical smell is an indicator that your pool needs to be cleaned.

pH Level

The pH level, which is the measure of how much basic or acidic chemicals your pool water contains, is another important metric. The pH level to aim for in your pool is around 7.2-7.8, which is slightly basic. Going much further toward either acid or base can be uncomfortable for swimmers and dangerous for your equipment.

pH is expressed as a number, with 7 as neutral, numbers less than 7 increasingly acidic, and numbers above 7 increasingly basic. Acids and bases can be equally irritating to skin, though slightly alkaline (basic) water is ideal for eyes and skin. Water with a pH lower than 7.2 tends to cause stinging eyes. Acids are also notorious for eating away at metal; even water as acidic as 6.8 can cause corrosion to pump and other metallic components over time. Water that is too basic can cause buildups of calcium that are very difficult to clean and can interfere with the function of pumps and other mechanical parts if the problem is allowed to go too far.


Balancing pH levels can be achieved by adding opposing chemicals to the water. Acids and bases cancel out, so by adding an acid to overly alkaline water, or a base to acidic water, the pH level can be adjusted to the appropriate level. Try muriatic acid to lower the alkalinity level, and borax to reduce acidity.

Total Alkalinity

The total alkalinity is related to pH levels. Each time an acid or base is added to the water to adjust pH levels, the total alkalinity of the water increases. This is a measurement of the neutralized acids and bases present in the water.

The higher the total alkalinity level of your pool, the more chemicals you will need to adjust the level further. A moderate total alkalinity is considered desirable; too high a total alkalinity means needing to use large amounts of chemicals to balance pH, while too low a total alkalinity makes pH change too quickly, requiring constant monitoring. The ideal is a pH level that is both flexible and stable.

To reduce the total alkalinity, the ratio of fresh water must be increased by draining some of the water and then refilling the pool. To increase total alkalinity, baking soda can be added to the water. Keep in mind that baking soda will also slightly lower pH, so do this step before adjusting the pH!


One chemical that gets less attention than most in pool chemistry is calcium. While calcium is not directly involved in the safety of the water for swimming, it is related to the safety of your pool. When water with a low level of calcium is kept in a pool for a long time, that water will naturally begin to saturate itself with calcium from all available sources. This means that your plaster, tile, stone, or other pool materials will gradually be eaten away.

The solution to this problem is to pre-saturate your water with calcium. Hard water with a high calcium level will not eat away at calcium sources, which will make your pool material last much longer. However, make sure not to let the calcium level get too high, or you may find it leaving deposits on the inside of your pump and other machinery. The ideal calcium level is between 250 and 350 parts per million. Calcium levels can be increased by adding calcium chloride dihydrate and can be decreased by partially draining and refilling the pool with fresh water.

Keeping pool chemicals in balance is a tough job, but the reward is well worth it. Monitor these important chemicals in your pool, and you will have a safe, clean, cool, comfortable place to swim in the summer. Make sure to get all the right chemicals to use in your pool installer,


or at your local pool supply store so that you will be ready for any situation!


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David Jackson, MBA

Financial lending analyst
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