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The alkalinity of your hot tub water needs to be between 80 and 120 ppm. If it is higher than that, here are some ways to lower it without affecting pH:
– Dilute the water by draining some out and replacing it with fresh water. This will dilute the alkalinity.
– Use an alkalinity decreaser chemical. These contain sodium bisulfate which lowers alkalinity without affecting pH.
– Use muriatic acid to lower alkalinity. Add small amounts and retest frequently to avoid lowering pH too much.
– Switch to a non-sodium alkalinity increaser when you need to raise alkalinity. Borate salts or potassium carbonate will raise alkalinity without impacting pH.
What is Alkalinity and Why is it Important?
Alkalinity refers to the ability of water to resist changes in pH. It is a measure of the buffering capacity of water or how much acid or base can be absorbed without causing a large change in pH.
In hot tubs, the alkalinity level is important for a few reasons:
– It helps keep the pH stable. Water with low alkalinity can cause the pH to swing up and down with use.
– It impacts the effectiveness of chemicals like chlorine or bromine. At low alkalinity, these sanitizers are less effective.
– It affects the calcium hardness saturation point. Calcium will have a greater tendency to precipitate out of solution at higher alkalinity.
The ideal alkalinity range for hot tubs is between 80 and 120 ppm (parts per million). Below 80 ppm, the pH becomes unstable and corrosion can occur. Above 120 ppm, the water is overbuffered and chemicals become less effective.
How to Test for Alkalinity
Testing alkalinity in a hot tub involves using an alkalinity test kit or test strips. Here is the process:
1. Get a water sample from the tub. Collect water from about 12-18 inches below the surface.
2. Add the alkalinity reagent to the sample per the test kit instructions. This will cause the sample to change color.
3. Compare the color to the scale provided to estimate the alkalinity level. Test kits may use drops, tablets, or test strips for the reagent.
4. Rinse the test tube and repeat if needed to verify the reading.
Test kits will provide a reading in ppm. Be sure to follow the instructions carefully for accurate results. Test alkalinity weekly to maintain proper levels.
Reading the Test Results
| Color | Alkalinity Level (ppm) |
| Yellow | 0 – 80 ppm |
| Green | 80 – 120 ppm (ideal) |
| Blue | 120 – 180 ppm |
| Pink | 180 – 240 ppm |
The color the water turns after adding reagent indicates the alkalinity level. Green indicates the ideal 80-120 ppm range.
How to Lower Alkalinity Without Affecting pH
If your hot tub alkalinity is reading high, here are some methods to lower it without disrupting the pH:
Dilute the Water
One straightforward way to reduce alkalinity is to drain some water out of the hot tub and add fresh water back in. This will dilute the mineral concentration and lower the alkalinity.
Drain 10-25% of the water from the tub. Refill with fresh water and retest alkalinity. You may need to repeat this process several times to reach the desired level.
This method is simple but does waste water. It also takes time to drain and refill the tub.
Use an Alkalinity Decreaser
Chemical alkalinity decreasers, also called alkalinity reducers, can lower alkalinity quickly without affecting pH. These contain sodium bisulfate, which lowers alkalinity without altering pH when used as directed.
Sodium bisulfate (NaHSO4) works by providing a source of hydrogen ions that react with carbonates and bicarbonates in the water to lower alkalinity. The sulphate ions help reduce alkalinity without consuming or generating hydroxide ions that would affect pH.
Follow the dosage instructions on the bottle carefully. Only use a small amount at a time and retest after each addition. Too much can quickly crash the alkalinity or pH.
Results should be seen in 1-2 hours after adding the chemical. Retest and add more if needed to reach the target alkalinity level.
Use Muriatic Acid
Muriatic acid, also called hydrochloric acid (HCl), can be used to lower alkalinity and pH together or alkalinity alone if added in small doses.
Since muriatic acid lowers both alkalinity and pH, it must be added slowly and levels rechecked frequently to avoid reducing pH too much.
Add 1/4 cup at a time, waiting 1-2 hours before retesting. Only add more if alkalinity is still high but pH is in range.
pH should be monitored at the same time as alkalinity and more sodium bicarbonate added if pH drops too low.
Muriatic acid can lower alkalinity quickly but requires close monitoring to avoid reducing pH too far.
Switch to Non-Sodium Alkalinity Increasers
To prevent alkalinity from getting too high going forward, switch to using non-sodium alkalinity increasers for maintenance.
Sodium bicarbonate and sodium carbonate are commonly used to raise alkalinity in hot tubs. However, the sodium ions contribute to high alkalinity.
Instead, use borate salts or potassium carbonate to raise alkalinity without impacting sodium levels.
Borate salts dissociate into boric acid, which maintains alkalinity through a pH-neutral buffering effect. Potassium carbonate provides carbonate alkalinity without sodium.
Regular use of these non-sodium alkalinity increasers will help keep levels from creeping up again once in range.
Preventing High Alkalinity
Once your alkalinity is lowered to the proper range, here are some tips to help prevent it from getting too high again:
– Test alkalinity before adding any chemicals. Only add alkalinity increaser if test shows it is needed.
– Use sodium bisulfate when adding sanitizer chlorine or bromine to compensate for their alkalinity increasing effect.
– Minimize use of pH increasers that contain sodium carbonate or sodium bicarbonate.
– Check alkalinity at least weekly and adjust as soon as it creeps out of range.
– Replace some hot tub water regularly to dilute dissolved minerals.
– Use a mineral cartridge filter or enzymatic filter cleaner to remove some minerals.
– When refilling, use a pre-filter on hose and balance water before adding to tub.
– Clean hot tub surfaces regularly to prevent scale buildup.
Conclusion
Maintaining proper alkalinity is crucial for hot tub water balance and sanitation. If alkalinity rises too high, it makes pH difficult to control and reduces the effectiveness of chemicals.
There are several good options for reducing alkalinity without lowering pH at the same time. Diluting the water, using alkalinity decreasers, or switching to non-sodium additive chemicals can all help lower and manage alkalinity levels.
Frequent testing and quick adjustment when out of range are key. With some attention and the right chemicals, you can keep your hot tub alkalinity in check.