When to drain and replace hot tub water
There is a formula for the number of daily users recommended by the National Swimming Pool Foundation (NSPF). The formula can be used to determine when hot tub water should be drained and replaced, which is as follows:
# of gallons in the hot tub ÷ 3 ÷ users per day = the number of days between draining
A hot tub in a semi-commercial or commercial facility needs to be maintained very differently and with much more attention than a residential unit. Only chemicals that are specifically designed for hot tubs are to be used. Chemicals should be used and added in moderation and dosing should be gradually broken up to avoid oversaturation and chemical reactions that can occur. Since a hot tub is a much smaller body of water, the saturation and water balance can be affected by chemical additions much faster than in a swimming pool. When using a sanitizer such as chorine (Cl), it is important to only use specific hot tub formulas. The use of calcium hypochlorite (Ca[ClO]2) should be avoided in hot tubs as the calcium byproduct can lead to cloudy water and increased potential for calcium carbonate scale. Non-petroleum natural-based clarifiers should be used to obtain clear water and avoid the buildup of oils and scum.
Soft water or softened water
“In hard water areas, can the hot tub be filled through a softener?” This question is frequently asked by hot tub owners. The answer is usually: “‘Soft’ water is corrosive and can damage equipment and surfaces, so one should never fill a hot tub through a water softener.” However, this is not true. There is a difference between naturally soft water and water from a softener.
Naturally soft water means the source water itself is lacking in sufficient minerals, such as calcium and magnesium. This water is largely present in regions where there is more rain and snow that gets into surface water, so there is very little mineral contact and absorption. Water that has been contained in the ground for longer periods has more time to absorb minerals in the earth and, therefore, will be hard.
When a water softener is used in hard water areas it displaces calcium ions with sodium ions to reduce the buildup of scale in the household. Naturally soft water is low in mineral content, pH, alkalinity, and total dissolved solids (TDS). However, water from a water softener still has sufficient levels of alkalinity and TDS, meaning it will not be corrosive. Filling a hot tub using a water softener can be beneficial as it reduces the calcium ions but still has enough buffer in the water to be safe.
| Is the water scale forming or corrosive? |
|---|
| Understanding the makeup of the source water can help in determining the best way to treat the hot tub from the first fill. The Langlier Saturation Index (LSI) is a tool professionals can use to determine if water has the potential to be scale forming (hard water) or corrosive (soft water).
The LSI works by using the test results of water balance as factors to determine the saturation of the water. The balance factors for LSI are as follows: pH, total alkalinity, calcium hardness, temperature, and total dissolved solids (TDS). Most test kit manufacturers can provide a chart that gives the numbers that correlate with the test results. Numbers from the LSI chart are matched to test results and then added together. The number for TDS is always subtracted from the total and that number depends on whether the TDS is over or under 1000 ppm. This formula will result in a number that will be on the plus or minus end. Any number over +0.3 would mean the water has the potential to be scale forming. A number below -0.3 means the water has the potential to be corrosive. Using this method, an operator can make changes to the water balance and re-calculate the numbers until they fall between the -0.3 to +0.3 range. This would mean the water is balanced. For details on the LSI, check with a test kit manufacturer. Know your sourceIt is vital to know the makeup of the source water. The most important factor is to know the total dissolved solids (TDS) of the source water. When hot tub water is 1500 ppm over the source water, then 50 per cent of sanitizer effectiveness can be lost. Based on this scenario, water should be diluted or drained when TDS levels are too high. |
