How to Chemically Balance Your Pool

1. The very first step in chemically balancing your pool is to know the volume (gallons) of your pool or spa!
  • using basic geometry you can find the cubic feet (ft3) of your pool by using this simple formula L x W x AD = Volume (ft3)
  • Assume the pool is rectangle in shape, measure the Length (max.) and Width (max,) and find the Average Depth  (deep end + shallow end)/2, now multiple all 3 together   L x W x AD  = Volume (ft3)
  • If you pool is shaped like something other then a rectangle then use one of these scaling factors.
    • Kiddney Shape- scaling factor (0.613)
    • Oval Shape - scaling factor (0.785)
  • To get the total gallons of water that is in your pool, just multiple your Volume (ft3) by 7.48 (1 ft3 = 7.48 gallons of water). For Liters (1 US gallon = 3.78541178 liter)
  • The idea is to get a general capacity of your pool to start with, this is just to give you a basic volume of your pool so that you will know how much chemicals to add so that you can bring you pool into balance.

Example: This pool is measured out to be 34'2" in Length, 15' in Width, and shallow end is 3'8" and deep end is 5'11"

use the eq. above 
(LxWxAD) = Volume

AD = (Deep end + Shallow end)/2

AD =(5.916ft + 3.666ft)/2=4.791ft


Gallons = 2455ft^3 x 7.48 =18363 gallons of water to fill this pool
Now this is a rough figure but it does give a starting point to work with.

2. The next step is to check your pools Alkalinity, Alkalinity effect your pH levels which in turn can effect your Sanitizer (Chlorine) levels. Alkalinity that is to high will make it difficult in adjusting your pH levels, Alkalinity that is to low will cause your pH levels to bounce or swing to high and to low, making them very unstable.

To increasing your total alkalinity using sodium bicarbonate

The recommended dosage when using baking soda (100% sodium bicarbonate) to raise your pool alkalinity for a certain volume of pool water.

Desired increase in PPM1,000 gallons5,000 gallons10,000 gallons20,000 gallons50,000 gallons100,000 gallons
10 ppm2.24oz11.2oz1.40lbs2.80lbs7.00lbs14.00lbs
20 ppm4.48oz1.402.80lbs5.60lbs14.0lbs28lbs
30 ppm6.72oz2.10lbs4.20lbs8.41lbs21lbs42lbs
40 ppm8.97oz2.80lbs5.60lbs11.2lbs28lbs56lbs
50 ppm11.2 oz3.50lbs7lbs14lbs35lbs70lbs
60 ppm13.4 oz4.20lbs8.41lbs16.8lbs42lbs84.1lbs

Now you should never try to add more than 10 pounds of sodium bicarbonate at any given time. The correct procedure would be to add what you can get away with, re-test after about 24 hours and then if more is needed, then you add again. It is possible that you may need to test and treat your recreational water facilities, for metals in solution before you can add any sodium bicarbonate.

A good practice to get into, is to premix or dissolve the baking soda in a bucket or mixing drum and then add the solution to the pool or spa. This procedure helps eliminate any signs of sodium bicarbonate from being visible at the bottom of your pool.

To decreasing your alkalinity using muriatic acid

Below is a table with the recommended dosage for using muriatic acid (31.45%), to decrease your TA for a given volume of pool water.

Desired increase in PPM1000 gallons5,000 gallons10,000 gallons20,000 gallons50,000 gallons100,000 gallons
10 ppm2.56fl oz12.8fl oz1.60pts1.60qts3.99qts2gals
20 ppm5.11fl oz1.60pts1.60qts3.20qts2gals4gals
30 ppm7.67fl oz1.20qts2.40qts1.20gals3gal6 gals
40 ppm10.2fl oz1.60qts3.20qts1.6gals4gals8gals
50 ppm12.8fl oz2qts4qts2gals5gals9.98-10gals

Whenever you attempt to lower your pool alkalinity, using muriatic acid, you should remember to add it at the deep end of your pool in pint size shots. Afterwards you should brush your pool/spa bottom to ensure that the acid does not settle in one area. The reason for this procedure is due to the fact that acid is heavier than water and will cause etching of pool surfaces.

***!!!*** Safety precautions when handling pool chemicals ***!!!***

When you have to deal with any type of pool or spa chemicals, you should always read the manufacturer's safety data sheets (MSDS). The information that they provide, will make you aware of the potential dangers of the product that you are dealing with.

3. The next step is to check your pools pH using any type of testing kits on the market. pH is the single most important element in swimming pool water chemistry. 

pH is a measure of hydrogen ion (H+) concentration in water. It indicates the relative acidity or alkalinity of the pool water. pH determines sanitizers (Chlorine) effectiveness which help the sanitizer kill the algae in your pool, pH is measured on a scale of 0 (strong acid) to 14 (strong base) with 7 being the neutral pH.

  • pH levels between 7.4 and 7.6 is normal!
  • 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!
  • Chart No. 1 - Raising pH with Soda Ash
    (If pH is under 7.4, add this amount of soda ash, then retest)

    7.2-7.42/3 oz.3 oz.6 oz.9 oz.12 oz.1 lb.2 lbs.
    7.0-7.23/4 oz.4 oz.8 oz.12 oz.1 lb.1 1/4 lbs.2 1/2 lbs.
    6.6-7.01 1/4 oz.6 oz.12 oz.1 lb.1 1/2 lbs.2 lbs.4 lbs.
    Under 6.71 1/2 oz.8 oz.1 lb.1 1/2 lbs.2 lbs.2 1/2 lbs5 lbs

  • If pH is too high - run acid demand test if available. pH is lowered by adding muriatic acid (hydrochloric 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.

    Chart No. 2 - Lowering pH with Muriatic Acid
    (If pH is over 7.6, add this amount of acid, then retest)

    7.6-7.81 1/4 oz.6 oz.12 oz.18 oz.24 oz.1 qt.2 qts.
    7.8-8.01 1/2 oz.8 oz.16 oz.24 oz.1 qt.1 1/4 qts.2 1/2 qts.
    8.0-8.42 1/2 oz.12 oz.24 oz.1 1/4 qts.1 1/2 qts.2 qts.1 gal.
    Over 8.43 oz.16 oz.1 qt.1 1/4 qts.2 qts.2 1/2 qts.1 1/4 gal.

4. After the pH step the second most important chemical in your Pool or Spa is Chlorine or sanitizers, if your pool already has a algae bloom or is in bad shape you must "Shock" your pool to eliminate the bloom. The best time to "shock" your pool is at night,  during the day sunlight (UV) will degrade the Chlorine in the pool making it less effective.

here is a basic overview of the type of Chlorine to look for in your pool.

Free Chlorine Residual is the amount of chlorine in the pool which has not reacted with substances other than water. It is the chlorine which is available to disinfect pool water and oxidize organic substances. Free chlorine residual should be maintained between 1 and 3 ppm.

Combined Chlorine is chlorine in the pool which has reacted with substance other than water and is no longer available in its free state. Some combined chlorines are bactericides but they contribute little to the disinfection process. Chlorine combined with ammonia produces chloramines which cause eye irritation and an objectionable chlorine odor. For this reason combined chlorine residual should be kept to a minimum preferably below 0.2 ppm.

Total Chlorine residual is the concentration of free chlorine plus combined chlorine. To determine combined chlorine residual test for free chlorine and total chlorine.

Total chlorine - free chlorine = combined chlorine

Breakpoint Chlorination is the process by which combined chlorine and some organics are "burned out" of the pool by addition of large amounts of chlorine. The reaction of chlorine with ammonia to form chloramines occurs in several stages with free chlorine consumed at each stage. If enough chlorine is added to the water the total chlorine residual will rise to a point that forces the reaction of chlorine with ammonia to go rapidly to completion. Compounds of nitrogen and chlorine are released from the water and the apparent residual chlorine decreases. The point at which the chlorine residual suddenly drops is called the breakpoint. When enough chlorine is added to pass the breakpoint, combined chlorine compounds disappear, eye irritation potential and chlorine odors disappear, and the chlorine remaining in the water is all in the free state.

Superchlorination: In order to prevent buildup of chloramines in the pool it is necessary to periodically add large amounts of new chlorine in an effort to pass the breakpoint. Public swimming pools should be supechlorinated about once a week. The amount of chlorine needed to reach the breakpoint will vary depending on the amount of organic material introduced by bathers and on the level of free chlorine maintained in the pool. If the amount of combined chlorine is known then the amount of new chlorine needed is ten times the amount of combined chlorine. When combined chlorine residual is not known, superchlorination is accomplished by adding 10 ppm of new chlorine to the pool. Ordinarily calcium hypochlorite at a dose of at least 1 lb. per 10,000 gallons is used for superchlorination. The chart below shows the amounts of various chlorine compounds which can be used to introduce 10 ppm of chlorine to the pool.

Chart No. 9 - Superchlorination
(Amount Needed to Introduce 10 ppm)
Type of chlorineGALLONS IN POOL
Sodium Hypo10 oz.1 3/4 qts.3 1/4 qts.1 1/4 gal.1 2/3 gal.2 gal.4 gal.
Lithium Hypo4 oz.1 1/4 lbs.2 1/3 lbs.3 1/2 lbs.4 3/4 lbs.6 lbs.12 lbs
Dichlor2 1/4 oz.11 oz.1 1/3 lbs.2 lbs.2 2/3 lbs.3 1/3 lbs.6 3/4 lbs.
Calcium Hypo2 oz.10 oz.1 1/4 lbs.2 lbs.2 1/2 lbs.3 1/4 lbs.6 1/2 lbs.

Non-chlorine Shock Treatments Several products have been developed which oxidize organics without the use of chlorine. Pools which use those products can accomplish the reduction of organics without closing the pool for any longer than it takes to dissolve and distribute the chemicals. Those products are more expensive than chlorine but may be preferred where it is necessary to keep a pool open.

How pH affects free chlorine residual Chlorine reacts with water to form Hypochlorous acid (HOC1). The reaction is different for each form of chlorine but hypochlorous acid is produced by each of those reactions and is the form in which chlorine serves best as a disinfectant. Hypochlorous acid is a weak acid and easily dissociates to an ionized hypochlorite state as shown below.

HOC1increasing pH->H+OC1-
Hypochlorous<-decreasing pHHydrogen+Hypochlorite

This is important because both hypochlorous acid and the hypochlorite ion are counted as free chlorine residual on your test kit but only the hypochlorous acid portion is an effective disinfectant. The balance between hypochlorous acid and the hypochlorite ion is affected by pH. The higher the pH, the less hypochlorous acid present and the less effective free chlorine becomes. At a pH of 7.2 about 66% of free chlorine is hypochlorous acid. At a pH of 7.8 only about 33% of free chlorine is hypochlorous acid. Thus pH control is essential for maintaining the effectiveness of chlorine as a disinfectant.

5. Also check Calcium Hardness

When we speak of scale, we are talking about calcium carbonate which has come out of solution and deposited itself on surfaces.  It is a combination of carbonate ions, a part of total alkalinity and calcium, and a part of the Calcium Hardness level.  The test for Calcium Hardness is a measure of how "hard" or "soft" the water is.  "Hard" water can have high levels of calcium and magnesium.  If these levels are too high, the water becomes saturated and will throw off excess particles out of solution which then seeks to deposit themselves on almost any surface inside the pool.  They can be attracted to ladders, lights and in extreme cases deposit themselves as very small crystalline clumps - all over the pool surfaces. Calcium Carbonate scale; a "white-ish," crystallized rough nodule.

If the Calcium Hardness levels are too low, the water is under-saturated.  If under-saturated, the water will become aggressive as it attempts to obtain the calcium it needs.  Such "soft-water" will actually corrode surfaces inside the pool which contain calcium (like pool plaster) and other minerals to maintain its hardness demand. 

If your Calcium Hardness levels are too high you can use a product called CalTreat to correct. Designed by United Chemical Corp., one bottle per 15000 gals can reduce Calcium Hardness levels within range.  In most cases you need not worry if your calcium levels are below 500, but much higher than that and it can cause pool problems. It can also be accomplished by dilution (adding water to the pool which has a lower calcium hardness content).  Levels which are too low require the addition of calcium chloride.  Recommended range for calcium hardness is 200-400ppm.  Calcium Hardness levels should be tested regularly

The Saturation Index

Also called the Langelier Index, this chemical equation or formula is used to diagnose the water balance in the aquatic environments (pools).  The formula is "SI = pH + TF + CF + AF - 12.1." 

To calculate the Saturation Index, test the water for pH, temperature, calcium hardness, and total alkalinity.  Refer to a chart for assigned values for your temperature, hardness, and alkalinity readings then add these to your pH value.  Subtract 12.1, which is the constant value assigned to Total Dissolved Solids and a resultant number will be produced.  A result between -0.3 and +0.5 is said to indicate balanced water.  Results outside of these parameters require adjustment to one or more chemical components to achieve balance.

This formula is not guaranteed; however, some readings for pH, calcium, and alkalinity which, if taken individually would be considered to be well beyond recommendations, can combine within the formula to produce "balanced water."  The SI can be used to pinpoint potential water balance problems  

**********IMPORTANT NOTE**********
All Chemicals added to the pool will change the ppm (Parts Per Million) ratio. when testing for a specific chemical and finding the ppm in your pool you must raise or lower that ppm by adding the correct chemicals. By converting the ppm to mg/L (milligrams per Liter) you can basically find the correct amount of chemicals to add to increase you ppm within your pool. Remember ppm = mg/L.