Water Balance
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 | ||
| Alkalinity | 80 to 120 ppm | Add Sodium Bicarbonate (Baking Soda) | Add Hydrochloric (Muriatic) Acid |
| pH | 7.4 to 7.6 | Add Soda Ash | Add Hydrochloric (Muriatic) Acid |
| Calcium Hardness | 150 to 400 ppm | Add Calcium Chloride | Dilute (add water) |
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.
- 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. These rapid fluctuations of pH levels are called pH bounces, and the result is a highly unbalanced water condition.
pH
pH is measured on a scale from 0 to 14:
- A pH of 7 is neutral.
- A pH below 7 is acidic.
- A pH above 7 is basic (alkaline).
The pH scale is logarithmic, which means for every whole unit of change, it's 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 (7.4 to 7.6) is very close to the pH of the human eye (7.5), which aides in swimmer comfort.
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.
Calcium Hardness
Details to follow.