Basic Pool Water Chemistry

Understanding basic pool water chemistry will help you keep your swimming pool safe for swimmers, reduces the amount of chlorine used, is the least corrosive to the equipment and pool shell, and is the cheapest way to own a pool.

Unbalanced water is expensive to balance, especially if algae have gotten out of control. If algae can grow easily, so can harmful bacteria. The water some area is naturally high in pH, for that reason we recommend the water be checked at least twice a week when the water is above 50°F, until the homeowner becomes more comfortable with the personality of the pool. Algae does not grow when water is below 50°F, while chlorine levels are not necessary to maintain in winter, keeping the rest balanced will preserve the equipment and pool shell.


Various test kits are available to help maintain basic pool water chemistry as well as testing stations in our pool store. For beginners, we recommend bringing water to our test station and getting dosing recommendations from our trained staff until enough test reports have built up to help with dosing on your own, once you begin testing the water yourself.

Free Chlorine
Range 0 – 1 2 – 4 5 – 10
Effects Algae & bacteria grow
Water unsafe
Eliminates bacteria
Dry skin
Faded suits
Red eyes
What to Add
to Adjust
Chlorine – tabs or shock Fresh water or time

Chlorine levels should be maintained when the water temperature gets above 50°. Depending on the weather, that can start as early as the end of February until the end of October.

If your swimming pool uses a different kind of sanitizer, check the owner’s manual for ideal levels and what is needed to adjust them.

Range 6.0 – 7.2 7.4 – 7.6 7.8 – 8.5
Effects Scale attaches to surfaces
Metals corrode
Plaster etches
Walls stain
Chlorine depletes rapidly
Chlorine most effective
Water is least corrosive
Mineral stay in solution
Chlorine ineffective
Minerals solidify
Water cloudy
What to Add
to Adjust
Soda Ash or Sodium BiCarbonate Muriatic Acid

Swimming Pools with salt systems will have to add extra acid to balance the pH. The chlorine compound that these systems add to the water has a pH of 11. As it chlorinates it is also raising the pH of the water.

Alkalinity and pH work with each other, with the same chemicals being used to adjust each of them. When needed, acid should be added in small doses so that the alkalinity is not effected dramatically. However, if both the pH and the alkalinity are high, a larger amount of acid can be added at one time.

Range 60 – 70 80 – 120 130 – 180
Effects pH varies wildly Keeps pH stable pH hard to adjust
What to Add
to Adjust
Soda Ash or
Sodium BiCarbonate
Muriatic Acid

Alkalinity and pH can be affected by rainfall. After a rain storm it is a good idea to test the water to see if it needs to be rebalanced.

Range 10 – 20 30 – 50 (Chlorine Tab Pools)
60 – 80 (Salt Pools)
90 – 150
Effects Chlorine dissipates
Allows water to hold chlorine so
that it can be used
Chlorine is blocked,
water cloudy
What to Add
to Adjust
Cyarunic Acid Add fresh water

Chlorine is used by algae, debris, bacteria and the sun. Stabilizer keeps the sun from using chlorine. Indoor swimming pools do not need as much. Stabilizer does not deplete like chlorine, it may only need to be added one to two times a year.


Total Hardness
Range 150 200 – 400 1000
Water pulls calcium from
Water is least
Scale attached to pool and
equipment surfaces
Water cloudy
Irritates eyes
What to Add
to Adjust
Calcium Chloride Fresh Water

Total Hardiness measures calcium, sodium and magnesium. Water that is not in the ideal range seeks to fill voids with the easiest sources, like the calcium in plaster walls or metals from screws and ladders.

Understanding and learning these basic pool water chemistry facts will help you maintain and have a perfectly clear swimming pool year after year.




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