Basic Pool Chemistry


Proper water chemistry is the most important factor when it comes to maximizing the life and appearance of any swimming pool. The following display references the most vital aspects of water chemistry as well as their proper ranges:

Factor                                Range

Free Chlorine                       1 - 3ppm

pH                                         7.2 - 7.8

Total Alkalinity                     80-120ppm

Calcium Hardness               200-300ppm

Stabilizer                              35-60ppm


PH Levels

PH is the measurement of the acidity of water — measured on a scale of 0 to 14, with 7 being neutral. A pH below 7.0 means the water is acidic, and as the pH approaches 8.0, the water becomes very more (alkaline).

A proper pH levels is essential in order for other chemicals to work correctly. Chlorine is much less effective at higher pH levels; at a pH of 8.0, chlorine is only 22% effective.

It is also important to note that low and high levels can cause damage to a vinyl liner. Under the right circumstances, when the pH is below 7.0, the liner can actually grow and develop unsightly wrinkles. A high pH will greatly accelerate the aging process and will shorten the life of the swimming pool liner. 


Total Alkalinity

Alkalinity is a measurement of the alkaline materials dissolved in water. Keeping your alkalinity level in the 80-120ppm range helps to stabilize the pH and prevent wild fluctuations. If the alkalinity is low, it can cause “pH bounce” — meaning the pH level fluctuates in and out of the acceptable range. Always adjust your alkalinity level before your pH!


Calcium Hardness

Calcium Hardness refers to the amount of dissolved minerals within the water. A low hardness level can lead to corrosion of the pool surface, filter, heater, ladder, etc. Likewise, if the water is too soft(low calcium level) you are also more likely to experience problems with algae. A calcium hardness level that is too high can cause cloudy water and scaling (a white chalky appearance).


Consequences of Unbalanced Pool Chemistry

·         Eye and skin irritation

·         Surface Staining and algae growth

·         Wrinkling of vinyl liners

·         Reduced efficiency of sanitizers

·         Corrosion of pool component metals (pump seals, heaters, lights, etc.)

·         Cloudy / turbid water

·         Scale build up (white chalky appearance) on pool surface as well as inside filter and heater

·         Pitting and corrosion of gunite/concrete/plaster pools


Water Out of Balance

A high pH, high Total Alkaline or High Calcium Hardness will cause cloudy water. Test and correct balance asap.



Algae is a possible cause of cloudy water. Algae can consume vast amounts of chlorine quickly.


Poor Filtration

Is the filter system running a significant number of hours every day? It is recommended that your filtration system run 10 to 12 hours per day depending on sun exposure. 


Pools with Cloudy Water or Visible Algae

·         Adjust pH to 7.2-7.6

·         Shock pool with double the normal dosage

·         Add algaecide

·         Vacuum pool to waste if possible when algae brushes off easily

·         After vacuuming (if not to waste) disassemble and thoroughly clean filter (cartridge or DE type filters) .

·         Add DE to filter through nearest skimmer if you have a DE type filter only


Metals & Staining

It is not uncommon to find metals, often called free metals, dissolved in pool water. Usually, they come from source / tap water, but sometimes come as a result of the erosion of metal pool fixtures, such as heat exchangers.

Free metals in pool water can cause staining of pool surfaces and inhibit the performance of water sanitizers. Ideally, there should be no metals in the water — 0 ppm. If metals are found in your water, you will need a sequestering agent to render them harmless.

The presence of metals in the water — such as iron (reddish-brown), copper (blueish-green), or manganese (brown-red) — can cause cloudiness and staining. To remove the metals:

·         Add sequestering agent

·         Add pool water clarifier

·         Run filter 1 or 2 hours; turn off pump overnight

·         Next day vacuum pool to waste

·         Add a stain and scale preventer to help remove any stains


Add Water-Balancing Chemicals Slowly

It is best practice to pre-dissolve a water balance adjustment chemical in a plastic bucket of pool water. Always add chemicals to water in a pail, never the other way around. Add chemicals to the deep end of the pool or in front of a return with the pump running.

PH Adjustment: Add recommended dosage, wait several hours and test water again. 
Alkalinity:   Add at the rate of 5 lbs. or less; wait about 10 minutes between each 5 lbs. 
Hardness: Add at the rate of 5 lbs. or less; wait 30 minutes between each 5. If large amounts of calcium are needed, add over several days.

Low pH and High Alkalinity  -      Adjust Alk first, Next Day pH

High pH Low Alkalinity         -       Adjust pH first, Next Day Alk

Low pH and Low Alkalinity  -       Adjust pH first, Next Day Alk

High pH High Alkalinity        -       Adjust Alk first, Next Day pH


Chlorine Stabilizer (Cyanuric Acid)

Stabilizer acts as a sun shield to extend the life of chlorine up to 3 1/2 times. It actually holds the useful form of chlorine in the pool water until needed, giving longer protection against bacteria and algae. It leaves no residue — 100% soluble. “Stabilized” chlorine products (sticks, tablets or chlorine powder) contain some cyanuric acid, which helps to maintain the proper level throughout the season.

Adding Stabilizer
Starting with a clean swimming pool, backwash the filter. Make a slurry of stabilizer and water, then add it very slowly through the closest skimmer to the pool equipment with the pump running.  Keep pump and filter running continuously for at least 48 hours. Do not backwash the pool filter for at least 3 or 4 days after adding stabilizer to pool.


Testing Pool Chemistry

·         Follow test kit instructions (test strips are more convenient but less accurate than kits)

·         Use fresh reagents - shelf life for liquid reagents is only one year.

·         Rinse out test cell with pool water before using.

·         Retrieve water sample at a depth of at least 12 inches from deep end of the pool

The Most Important Poolside Tests: Free Chlorine level, pH level and Total alkalinity. Free chlorine is the unused, effective chlorine that you want in your pool. pH  levels can fluctuate due to weather and swimmer related influences, some of which include rain, swimmer wastes, refill water, and the pH of various pool chemicals, including some of the following well know pool products:

·         CALCIUM  HYPOCHLORITE  – pH 11.7


·         BROMINE TABLETS – pH 3.6

·         SODIUM DICHLOR – pH 7.0

·         LITHIUM HYPOCHLORITE – pH 10.5



Types of Algae

Mustard Algae: Common algae in pools appears yellow-brown or “mustard” colored. It brushes off the walls of the pools easily, but quickly returns. It often grows in shady areas with poor circulation. It often resists chlorine and shock treatment.

Solution: Use an algaecide along with chlorine shock. Follow label directions. Place all vacuum equipment — hose, head, pole, brushes, etc. — into pool during treatment. Maintain a higher than normal chlorine reading for 4 to 5 days after treatment.

Green Algae: Green algae is one of the most common problems pool owners encounter. It usually appears in corners or other areas where circulation is poor. Once established, green algae can grow explosively.

Solution: Use Algaecide along with chlorine shock. Follow label directions. It is also sometimes recommended to use a flocking agent. Always vacuum to waste or drain (not backwash).

Black Algae: A very resistant form of algae that clings to the pool’s walls, floor and cracks. The longer black algae are present, the longer it will take to get rid of them. Black algae can actually pit the marcite finish in a gunite pool. Treat black algae as soon as it is detected. Black algae are usually found in gunite/concrete pools.

Solution: Brush algae spots vigorously with a stiff algae brush and pour algaecide along the sides where spots are visible. Run filter continuously for one hour, and then add chlorine shock to the pool.


Preventing Algae Basics


Maintain a proper chlorine reading


Brush walls and pool floor

Vacuum pool / Run Polaris or other pool cleaner

Use a maintenance dose of Algaecide

Keep pool properly balanced – recommended readings: Free Chlorine: 1.0-3.0, pH: 7.2-7.8, Total Alkalinity: 80-120ppm, Hardness: 200-300ppm, Stabilizer: 35-50ppm