Water Balance
The contents in the sections below are attributed to multiple sources. While it's intended to be as accurate as possible, Fairway Farms Swim Club makes no guarantees of its accuracy. The content is to be used for reference purposes only.
Chemical quantities are based on a rounded figure of 200,000 gallons for the pool capacity (203,950 on the original drawings, not including volume within piping).
Overview
One of the most important parts of running a pool is keeping the water balanced. Unbalanced water can cause damage to concrete, grout, marcite (pool plaster) and metals. Water can corrode surfaces or deposit substances called scale.
Unbalanced or "aggressive" water can also destroy filters and copper heat exchangers. One way to identify corrosive water is by staining, which a deposit of colored metal salts of iron (brown) or copper (blue, green, grey or black). Scaling water does the opposite - it attempts to deposit or precipitate calcium carbonate out of the water, causing deposits on the surface and plugging of the filters and piping.
| Parameter | Ideal Range | Method to Adjust | |||
|---|---|---|---|---|---|
| Increase | Decrease | Calcium Hardness | 150 to 400 ppm | Add Calcium Chloride | Dilute (add water) |
| Chlorine (minimum) without Cyanuric Acid |
1.0 ppm (pH: 7.2 to 7.5) 2.0 ppm (pH: 7.6 to 8.0) |
Add Chlorine | Dilute (add water) | ||
| Chlorine (minimum) with Cyanuric Acid |
2.0 ppm (pH: 7.2 to 7.5) 4.0 ppm (pH: 7.6 to 8.0) |
Add Chlorine | Dilute (add water) | ||
| Cyanuric Acid (stabilizer) | Up to 40 ppm (per Chemtrol) | Add Stabilizer (Cyanuric Acid) | Dilute (add water) | ||
Measurement and Adjustment Order
As important as it is to adjust these factors to maintain water balance, the sequence is the most important:
- Total Alkalinity is always the first parameter to be corrected. Exceptions can be made when pH drops to a very low level or if metals are present in the water.
- Then, adjust pH (in our pool, this is managed automatically by the Chemtrol Pool Controller).
- Finally, adjust Calcium Hardness.
When lowering calcium hardness by diluting the water, pH and total alkalinity are adjusted after the dilution has been completed.
Total Alkalinity
Total alkalinity is the measure of the water's ability to "buffer" from wide pH swings. A buffer is a chemical system that resists change when acids or bases are added to the water. In water with no buffer ability, pH can shift dramatically. This rapid fluctuation of pH is called pH bounce, and the result is a highly unbalanced water condition.
| Ideal Range | 80 to 100 ppm |
|---|---|
| To Increase | Add sodium bicarbonate (baking soda) 28 lbs for +10 ppm 50 lbs for +17.9 ppm (10 ppm/1.4 lbs for 200,000 gallons) |
| To Decrease | Usually not necessary; will decrease with the addition of acid. |
Per PHTA, alkalinity should ideally be kept between 80 and 100 ppm when calcium hypochlorite is used as a sanitizer. Worst case, it must be no less than 60 and no greater than 180. More broadly speaking, a range from 80 to 120 is often cited as acceptable. The state and county do not appear to have a standard that supersedes this guideline.
| Low Total Alkalinity | High Total Alkalinity | |
|---|---|---|
| Impact |
|
|
| Non-Balance Problems | pH bounce | pH drifts upward |
Testing
Total alkalinity, like calcium hardness, is tested by titration. At the endpoint the color changes from green to red. Make sure to follow the directions on the inside of the test kit thoroughly. Observe that some samples will turn from green to purple instead of green to red. This color change can also be used as a reliable endpoint. It is caused by the use of a polymeric biguanide (PHMB) in the pool.
False Readings
The most common problem in the total alkalinity test is caused by a high level of chlorine. When excessive chlorine is present in the sample, one of the two reagents used in the total alkalinity indicator will bleach out. When this happens, the endpoint changes from blue to yellow instead of green to red. To avoid this problem, repeat the test with an extra drop of the first reagent, thiosulfate. This should destroy the excess chlorine and solve the problem.
Adjustment
Pour bag(s) of sodium bicarbonate slowly into the surge tank. This should ideally be done late in the day to allow it to dissolve overnight. After pouring, the Chemtrol may briefly alarm due to the elevation of pH and TDS (conductivity) readings due to the spike in concentration within the filter system. The alarm should clear after several minutes.
If possible, use the full bag to avoid keeping partial bags on-hand.
Sodium bicarbonate can be purchased for about $40 from Aquatic Source in Brighton (plus delivery charge) or B&B Pools in Livonia.
Re-test alkalinity after six hours.
pH
pH is the "potential of Hydrogen"; a scale specifying the acidity or basicity of a solution, measured on a scale from 0 to 14:
| Ideal Range | 7.4 to 7.6 |
|---|---|
| To Increase | Add Soda Ash (usually not necessary) |
| To Decrease | Add Hydrochloric (Muriatic) Acid (should be automatically dispensed) |
Testing
pH is a colorimetric measurement that uses a color indicator to identify pH ranges. Most tests use phenol red, with a test range of 6.8 to 8.4. When testing pH, it is important to carefully understand and follow the directions provided with test kit.
False Readings
Sometimes, high levels of chlorine will quickly convert phenol red into a new indicator that is dark purple when the pH is above 6.6. A common mistake would be to confuse the purple color for dark red and wrongly add acid to the pool.
Background
- A pH of 7 is neutral.
- A pH below 7 is acidic.
- A pH above 7 is basic.
The pH scale is logarithmic, which means for every whole unit of change, it is ten times different than the prior value.
Examples:
- A pH of 6 is 10 times more acidic than than a pH of 7.
- A pH of 4 is is 100 times more acidic than a pH of 6.
The ideal range of pH is targeted to be 7.4 to 7.6. A common myth is that this is very close to the pH of the human eye, often cited as having a pH of 7.5. However, this isn't quite the case.
Calcium Hardness
Water that has little calcium or magnesium in it is called soft. Hard water contains high levels of calcium and magnesium salts and consumes soap, making it hard to form suds. In pools, having too much calcium may cause the water to scale. Having little to no calcium can cause the water to become corrosive or "aggressive" and may eat away at concrete, marcite (pool plaster) or grout.
| Low Calcium Hardness | High Calcium Hardness | |
|---|---|---|
| Impact |
|
|
Testing
Calcium hardness is tested by titration with an endpoint that changes from red to blue. Be sure to follow the directions on the inside of the test kit thoroughly.
False Readings
The most common error in testing calcium hardness is called a fading endpoint. Instead of observing a well-defined color change and a permanent endpoint, some color change occurs, but the sample then reverts back to its original color. This usually happens due to small concentrations of iron or copper in the pool water, causing the the test to turn purple instead of blue. To remedy, add five or six drops of the titrant to the water sample first, then conduct the test as usual. When a complete color change is observed, add up the drops (including the five or six initially added) to obtain a total. The initial five or six drops act as a bonding agent, holding together the interfering metals so the color change is apparent and the test is conclusive.