Guide to Pool Water Chemistry & Pool Water Care

Water care and chemical balance is perhaps the largest single determiner of the safe use, appearance and life of your pool. 

We’ve pulled together, for your easy reference, what you need to know along with some expanded information and explanations about managing your swimming pool water chemistry.

Pool Water Chemistry

  • Eye and skin irritation
  • Staining
  • Corrosion of metals (pump seals, heaters, lights, etc
  • Cloudy water
  • Scale build-up appearing as a white chalky powder on pool surfaces
  • Pitting and corrosion of concrete pool surfaces such as plaster
  • Wrinkling, staining or fading of vinyl pool liner
  • Skin & eye irritation

Factor                                         Range                                                Frequency

Free Chlorine                         1.0 to 3.0                                           Daily

PH                                                7.2 to 7.6                                            Daily

Total Alkalinity                     80 to 120 ppm                                Weekly               

Calcium Hardness              200 to 300 ppm                             Monthly

Stabilizer                                  25 to 50 ppm                                   Monthly

The chlorine that is free or available to sanitize your pool. This is what you measure when testing your pool water. When you add chlorine, you’re increasing the amount of free chlorine in the water.  Free chlorine levels between 1 and 3 parts per million (ppm) is acceptable with the ideal level being 2 ppm.

The chlorine that is combined with contaminants such as nitrogen and ammonia through oxidization. In the process of oxidization, free chlorine combining with contaminates, becomes combined chlorine.  Combined chlorine remains in the water and with a reduced ability to oxidize additional contaminates.

The sum of the Free Chlorine and Combined Chlorine in the pool water.

Total Chlorine = Free Chlorine + Combined chlorine

  • The measurement of acidity level in the water
    • Measured on a scale of 0 to 14
      • =< 7.1 – Acidic
      • 7.2 to 7.6 – Ideal Range
      • => 7.7 – Basic or Alkaline
  • Proper PH levels optimize the effectiveness of other chemicals. Chlorine is much less effective when the PH level of the water is high. For example chlorine is ~80% less effective in terms of oxidization at a PH level of 8.0
  • Improper PH levels in swimming pool water can cause damage to the surfaces the water comes in contact with, in particular, vinyl pool liners.

Total Alkalinity is a measurement of the alkaline substances in the water.  Separate from PH, alkalinity has a direct effect on the pool water’s PH.  Ideally, a range of 80 to 120 ppm helps to control PH fluctuations. If the Total Alkalinity level is low it can cause a “pH bounce” causing the pH level to fluctuate in and out of the acceptable range. When Total Alkalinity is high it can cause the water to become cloudy and cause lime precipitates.

Sometimes referred to as Total Hardness is a measure of the amount of lime dissolved in the water. Water with a calcium hardness of less than 100 ppm is described as soft water. Soft water can draw lime out of tile grouting, plaster and concrete of gunite pools.  Low Calcium Hardness can lead to disintegration of the grout, plaster and/or concrete matrix of gunite pools.  Water with a calcium hardness above 300 ppm 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 200-300 ppm.

Stabilizer, sometimes referred to as ‘pool water conditioner’ or ‘conditioner’ is typically 100% Cyanuric Acid.  Stabilizer binds chlorite to ions in free chlorine which allows the chlorine to withstand the UV rays of the sun, which would otherwise break the chlorite ions apart and allow the chlorine to evaporate.  Cyanuric Acid ‘stabilizes’ the chlorine ion extending the life or oxidation reduction potential (ORP) of the free chlorine by 3 times to 5 times.  Stabilizer is typically added to the water initially and then maintained through the use of ‘stabilized’ chlorine.

Vinyl Pool Liner Care Quick Reference

Factor                                  Range                                          Frequency

Free Chlorine                         1.0 to 3.0                                           Daily

PH                                                7.2 to 7.6                                            Daily

Total Alkalinity                     80 to 120 ppm                                Weekly               

Calcium Hardness              200 to 300 ppm                             Monthly

Stabilizer                                  25 to 50 ppm                                   Monthly

Maintain free chlorine residual between 1.0 and 3.0 ppm.  If free chlorine drifts below 1.5 ppm, algae and bacterial growth can take hold more easily and may cause staining of the vinyl liner.

A low pH of less than 7.0 should be especially avoided, since it can cause the liner to form wrinkles.  To reduce the effects of low PH, it is recommended that all vinyl lined swimming pools be routinely stabilized so that a minimum of stabilizer level of 50 ppm is maintained.

Pre-dissolve slow dissolving sanitizers in a bucket of pool water and add the solution to the pool by filtering through a sieve to prevent non-dissolved particles from settling on the bottom, otherwise spot bleaching of the liner could occur. Always read and follow manufacturer’s instructions given on product labels and containers.

Test for the presence of dissolved metals in pool water. Dissolved metals may cause staining of the vinyl liner directly or may combine with calcium hardness and form discoloured deposits on vinyl liner. Follow manufacturer’s recommendation concerning the use of chelating materials to inactivate dissolved metals.

Chemicals should never be mixed together and added to the pool water at the same time. Certain combinations of the chemicals that individually will have no effect can cause bleaching of the liner if concentration is allowed to remain high in the vicinity of the liner. Always allow a chemical to disperse throughout the pool by means of water recirculation, before adding a second chemical.

Do not drain the pool completely for any reason without consulting a Pool Fits pool professional for advice. The older the liner, the higher the risk that the liner will shrink and not stretch back into its original shape without ripping. Sites with a high water table may also carry the additional risk of structural damage to the pool.

Never close a pool without circulating the pool water for a minimum of hours after the final addition of chemicals. Even liquid chlorine can concentrate in the deep end and cause liner bleaching, if not sufficiently blended with the rest of the pool water.

Use a well-fitting winter pool cover that is tightly sealed around the entire perimeter of the pool to prevent accumulation of debris such as leaves, worms, etc. during the winter period. Organic matter has the potential to cause staining and/or bleaching of the vinyl liner.

Avoid the use of abrasive cleaning agents or cleaning aids (such as steel wool, sharp bristled brushes, scouring pads, etc.)

Use only manufacturer’s recommended vinyl liner cleaner for removing accumulated soil at water line or other soiled areas.