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Water Quality

balancing your pool & spa water

Proper water chemistry is essential to maintaining safe and consistent swimming pool operation. Chemicals used in swimming pools include: sanitizers or disinfectants to destroy harmful or otherwise objectionable organisms; Alkalinity and pH Adjusters to maintain a consistent acid-base relationship; Chlorine Stabilizer to prevent unnecessary loss of chlorine; Algicide to kill and prevent algae, and Filter Aids to help remove foreign material.

The following information has been compiled from several documents and sources written by professionals in the industry. It is about the various factors which affect water chemistry, how they affect swimming pools and how to use pool chemicals to restore properly balanced swimming pool and spa water chemistry. We hope that is of help to you. While the importance of keeping our pools and spas safe and healty for our use cannot be overlooked, we want to encourage you to undertake this responsibility with the spirit of fun and relaxation that is implied in the theme of water fun and sports. Enjoy! If you ever need assistance, we are dedicated to serving our community with friendly and responsive communication. Feel free to call with any questions or comments.

pH

pH is the single most important element in swimming pool water chemistry. It affects every other chemical balance in pool water.
pH is a measure of hydrogen ion concentration in water. It indicates the relative acidity or basicity of pool water. pH is measured on a scale of 0 (strong acid) to 14 (strong base) with 7 being the neutral pH.
In pools a slightly alkaline pH of 7.4 to 7.6 is most desirable because this range is most comfortable to the human eye and provides for optimum use of free chlorine while maintaining water that is not corrosive or scale forming.


If pH is too low (below 7)

  • Water becomes acidic
  • Chlorine dissipates rapidly
  • Eye irritation occurs
  • Plaster walls are etched
  • Metal fittings, pump impeller, heater core may corrode
  • Dissolved metals may leave stains on walls
  • Rapid Loss of alkalinity

If pH is too high (above 8)

  • Chlorine activity is slowed and inefficient
  • Scale formation and discoloration of pool walls
  • Water becomes cloudy
  • Filter is overworked
  • Eye irritation may occur

pH Adjustment


To avoid the problems listed above, pH must be maintained between 7.2 and 7.8. The most desirable level for pH is between 7.4 and 7.6. If pH is too low - run alkali demand test if available. Raise pH by adding soda ash (sodium carbonate). Never add more than 2 lbs per 10,000 gallons in a single treatment. Be sure the pump is running when chemicals are added. Allow to recirculate then retest to determine if further treatment is necessary. Caustic soda (sodium hydroxide) is sometimes used with chemical feed pumps to raise pH. If problems with low pH persist, it may be necessary to raise total alkalinity to stabilize the pH.

factors which affect pH

Lowers pH

 

Raises pH

Acid

 

Soda Ash

Gas Chlorine

 

Sodium Hypochlorite

Trichlor Chlorine

 

Calcium Hypochlorite

Dichlor Chorine

 

Caustic Soda

Rain Water

 

Bicarbonate of Soda

Alum

 

Swimmer Wastes

Organic Litter

 

Algae Growth

Make up Water

 

Make up Water

raising pH with Soda Ash

(If pH is under 7.4, add this amount of soda ash, then retest)

 

GALLONS IN POOL

pH

1,000

5,000

10,000

15,000

20,000

25,000

50,000

7.2-7.4

2/3 oz.

3 oz.

6 oz.

9 oz.

12 oz.

1 lb.

2 lbs.

7.0-7.2

3/4 oz.

4 oz.

8 oz.

12 oz.

1 lb.

1 1/4 lbs.

2 1/2 lbs.

6.6-7.0

1 1/4 oz.

6 oz.

12 oz.

1 lb.

1 1/2 lbs.

2 lbs.

4 lbs.

Under 6.7

1 1/2 oz.

8 oz.

1 lb.

1 1/2 lbs.

2 lbs.

2 1/2 lbs

5 lbs

lowering pH with Muriatic Acid

If pH is too high - run acid demand test if available. pH is lowered by adding muriatic acid or sodium bisulfate. Carefully add acid at the deep end of the pool. Try not to pour acid near pool walls or fittings. Remember: When using or diluting acids," do as you oughta, add the acid to the water" (never add water to acid)
NOTE: 10 lbs. sodium bisulfate is roughly the same as 1 gal. muriatic acid.
(If pH is over 7.6, add this amount of acid, then retest)

 

GALLONS IN POOL

pH

1,000

5,000

10,000

15,000

20,000

25,000

50,000

7.6-7.8

1 1/4 oz.

6 oz.

12 oz.

18 oz.

24 oz.

1 qt.

2 qts.

7.8-8.0

1 1/2 oz.

8 oz.

16 oz.

24 oz.

1 qt.

1 1/4 qts.

2 1/2 qts.

8.0-8.4

2 1/2 oz.

12 oz.

24 oz.

1 1/4 qts.

1 1/2 qts.

2 qts.

1 gal.

Over 8.4

3 oz.

16 oz.

1 qt.

1 1/4 qts.

2 qts.

2 1/2 qts.

1 1/4 gal.

total alkalinity (TA)

Total alkalinity is a measure of water's resistance to change in pH. Total alkalinity is closely associated with pH, expressed in parts per million (ppm). Total alkalinity is the result of alkaline materials including carbonates, bicarbonates and hydroxides. This acid neutralizing (buffering) capacity of water is desirable because it helps prevent wide variations in pH whenever small amounts of acid or alkali are added to the pool.
Total alkalinity should be maintained in the range of 80 to 150 ppm.
If total alkalinity is too low:
pH changes rapidly when chemicals or impurities enter the water. pH may drop rapidly, causing etching and corrosion.
If total alkalinity is too high:
pH becomes difficult to adjust. High pH often occurs causing other problems such as; cloudy water, decreased disinfectant effectiveness, scale formation and filter problems.

raising Alkalinity using Sodium Bicarbonate

Total alkalinity can be raised by the addition of bicarbonate of soda (sodium bicarbonate, baking soda). 1.4 lbs. bicarbonate of soda per 10,000 gallons will raise total alkalinity 10 ppm.

Increase

GALLONS IN POOL

(ppm)

1,000

5,000

10,000

15,000

20,000

25,000

50,000

10

0.14 lbs

0.7 lbs.

1.4 lbs.

2.1 lbs.

2.8 lbs.

3.5 lbs.

7 lbs.

20

0.28 lbs.

1.4 lbs.

2.8 lbs.

4.2 lbs.

5.6 lbs.

7.0 lbs.

14 lbs.

30

0.42 lbs.

2.1 lbs.

4.2 lbs.

6.3 lbs.

8.4 lbs.

10.5 lbs.

21 lbs.

40

0.56 lbs.

2.8 lbs.

5.6 lbs.

8.4 lbs.

11.2 lbs.

14.0 lbs.

28 lbs.

50

0.70 lbs.

3.5 lbs.

7 lbs.

10.5 lbs

14.0 lbs.

17.5 lbs.

35 lbs.

raising Alkalinity using Soda Ash

In some cases, soda ash can be used to raise total alkalinity. Pound for pound, soda ash raises alkalinity 60 percent more than sodium bicarbonate and is cheaper than sodium bicarbiante. The problem with using soda ash to increase alkalinity is it drastically increases pH. This can cause cloudy water and scale formation. Soda ash should only be used to increase total alkalinity if you also need to increase the pH or if only small increases in alkalinity are needed.


Increase

GALLONS IN POOL

(ppm)

1,000

5,000

10,000

15,000

20,000

25,000

50,000

10

0.09 lbs

0.44 lbs.

0.88 lbs.

1.32 lbs.

1.77 lbs.

2.21 lbs.

4.42 lbs.

20

0.18 lbs.

0.88 lbs.

1.77 lbs.

2.65 lbs.

3.53 lbs.

4.42 lbs.

8.83 lbs.

30

0.26 lbs.

1.32 lbs.

2.65 lbs.

3.97 lbs.

5.30 lbs.

6.62 lbs.

13.25 lbs.

40

0.35 lbs.

1.77 lbs.

3.53 lbs.

5.30 lbs.

7.07 lbs.

8.83 lbs.

17.66 lbs.

50

0.44 lbs.

2.21 lbs.

4.42 lbs.

6.62 lbs.

8.83 lbs.

11.04 lbs.

22.08 lbs.

raising Alkalinity using Sodium Sesquicarbonate

Chemical manufactures are now marketing a total alkalinity increaser which combines the effects of sodium bicarbonate and soda ash. The product sodium sesquicarbonate or sodium hydrogen carbonate affects total alkalinity more than sodium bicarbonate, but does not cause quite as much increase in pH as soda ash does.

Increase

GALLONS IN POOL

(ppm)

1,000

5,000

10,000

15,000

20,000

25,000

50,000

10

0.13 lbs.

0.63 lbs.

1.25 lbs.

1.88 lbs.

2.50 lbs.

3.13 lbs.

6.25 lbs.

20

0.25 lbs.

1.25 lbs.

2.50 lbs.

3.75 lbs.

5.00 lbs.

6.25 lbs.

12.50 lbs.

30

0.38 lbs.

1.88 lbs.

3.75 lbs.

5.63 lbs.

7.50 lbs.

9.38 lbs.

18.75 lbs.

40

0.50 lbs.

2.50 lbs.

5.00 lbs.

7.50 lbs.

10.00 lbs.

12.50 lbs.

25.00 lbs.

50

0.63 lbs.

3.13 lbs.

6.25 lbs.

9.38 lbs.

12.50 lbs.

15.63 lbs.

31.25 lbs.

lowering Alkalinity using Muriatic Acid

Total alkalinity can be lowered by adding muriatic acid or sodium bisulfate. Acid may be added in doses of up to 1 quart per 10,000 gallons. Total alkalinity tests and further required additions of acid can be made every 2 hours.


Decrease

GALLONS IN POOL

(ppm)

1,000

5,000

10,000

15,000

20,000

25,000

50,000

10

2.56 oz.

0.8 pts.

0.8 qts.

1.2 qts.

1.6 qts.

2.0 qts.

1 gal.

20

5.12 oz.

1.60 pts.

1.6 qts.

2.4 qts.

3.2 qts.

1.0 gal.

2 gal.

30

7.68 oz.

1.2 qts.

2.4 qts.

3.6 qts.

1.2 gal.

1.5 gal.

3 gal.

40

10.24 oz.

1.6 qts.

3.2 qts.

1.2 gal.

1.6 gal.

2.0 gal.

4 gal.

50

12.80 oz.

2.0 qts.

1.0 gal.

1.5 gal.

2.0 gal.

2.5 gal.

5 gal.

lowering Alkalinity using Sodium Bisulfate


Decrease

GALLONS IN POOL

(ppm)

1,000

5,000

10,000

15,000

20,000

25,000

50,000

10

0.21 lbs.

1.06 lbs.

2.13 lbs.

3.19 lbs.

4.25 lbs.

5.31 lbs.

10.63 lbs.

20

0.43 lbs.

2.13 lbs.

4.25 lbs.

6.38 lbs.

8.50 lbs.

10.63 lbs.

21.25 lbs.

30

0.64 lbs.

3.19 lbs.

6.38 lbs.

9.56 lbs.

12.75 lbs.

15.94 lbs.

31.88 lbs.

40

0.85 lbs.

4.25 lbs.

8.50 lbs.

12.75 lbs.

17.00 lbs.

21.25 lbs.

42.50 lbs.

50

1.06 lbs.

5.31 lbs.

10.63 lbs.

15.94 lbs.

21.25 lbs.

26.56 lbs.

53.13 lbs.

the role of calcium hardness

Calcium hardness is a measure of the dissolved calcium salts in water. Under normal conditions this should not be a problem in properly operated swimming pools. Estimates of the proper range of calcium hardness vary widely but the ideal level for plaster pool is generally considered to be about 250 ppm. If calcium hardness is very low then water may leach calcium from pool walls causing pitting of the plaster surface. Very high calcium hardness may contribute to scale formation and clouding of the water. To raise calcium hardness - add calcium chloride.

raising hardness with Calcium Chloride


Increase

GALLONS IN POOL

(ppm)

1,000

5,000

10,000

15,000

20,000

25,000

50,000

10

2 oz.

10 oz.

1 1/4 lbs.

1 3/4 lbs.

2 1/2 lbs.

3 1/4 lbs.

6 1/4 lbs.

20

4 oz.

1 1/4 lbs.

2 1/2 lbs.

3 3/4 lbs.

5 lbs.

6 1/4 lbs.

12 1/2 lbs.

30

6 oz.

1 3/4 lbs.

3 3/4 lbs.

5 1/2 lbs.

7 1/2 lbs.

9 1/2 lbs.

18 3/4 lbs.

40

8 oz.

2 1/2 lbs.

5 lbs.

7 1/2 lbs.

10 lbs.

12 1/2 lbs.

25 lbs.

50

10 oz.

3 lbs.

6 1/4 lbs.

9 1/2 lbs.

12 1/2 lbs.

15 3/4 lbs.

31 1/4 lbs.

To lower calcium hardness anhydrous trisodium phosphate may be used. One pound trisodium phosphate per 10,000 gallons will lower calcium hardness 11 ppm. Use in small increments or clouding may occur. Another method of lowering calcium hardness is to simply drain off part of the pool water and dilute the remaining water with fresh make up water.

total dissolved solids (TDS)

After a pool has been in use for a time, dissolved solids may begin to accumulate. These unfilterable solids include body wastes, suntan lotion, stabilizer, chlorines, algicide, dirt, pollen, etc. Normally this is less of a problem with outdoor pools because of rain water and no use during winter months. Indoor pools sometimes have a buildup of dissolved solids requiring draining the pool and refilling with fresh water. Most pools should be drained after 3 to 5 years. Spas are less of an issue, as they are typically refilled about once every 4-6 months. Thus the TDS does not have a chance to really become a serious problem.

Ideally pool water contains under 450 ppm total dissolved solids. This test must be done with special meter that reads the dissolved solids and while it is a valuable water quality test, it is not common among the test tools for most residential pools. The device is available for purchase and if you are into making sure your pool or spa is doing it's very best for you, then buying this extra equipment may be of interest to you. It is a required test for public swimming pools in the U.S.