Having the right alkalinity level is crucial for keeping your hot tub water balanced and sanitized. If the alkalinity gets too high, it can cause a number of issues that may damage your hot tub and create discomfort for bathers. In this article, we’ll look at the causes and effects of high alkalinity in hot tubs, how to test for it, and what you can do to lower alkalinity levels back to the proper range. Keep reading to learn more!
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What is Alkalinity in a Hot Tub?
Alkalinity refers to the amount of bicarbonates, carbonates, and hydroxides present in hot tub water. These alkaline compounds act as a buffer, preventing the pH from fluctuating too much when chemicals or bather loads change.
The ideal alkalinity range for most hot tubs is 80-120 parts per million (ppm). This level provides enough buffering capability to keep the pH stable, without being so high that it causes other problems.
Causes of High Alkalinity
There are a few key causes that can lead to high alkalinity in your hot tub:
Using too much alkalinity increaser
Adding too much sodium bicarbonate (baking soda) or sodium carbonate to raise alkalinity can easily cause it to become too high. Always follow dosage recommendations carefully when using alkalinity increaser chemicals.
Low bather load
With fewer people soaking in the tub, there is less acid from bathers’ skin and sweat to naturally lower the alkalinity. Lighter bather loads mean the alkalinity can more easily climb higher than desired.
Infrequent water changes
Over time, the concentration of alkaline compounds increases as water evaporates but these dissolved solids remain. Failing to drain and refill the tub periodically allows alkalinity to creep upwards.
High pH
When the pH is too high (above 7.6), more of the alkalinity is present in the form of carbonates rather than bicarbonates. Carbonates increase total alkalinity measurements, so high pH can contribute to high alkalinity.
High calcium hardness
Calcium from dissolved calcium chloride or calcium carbonate causes additional carbonates to form, which boosts total alkalinity.
Excessive use of lithium bromide
This chemical is added to some hot tubs to help prevent foaming. However, lithium bromide dissociates into lithium hydroxide in water, which raises the alkalinity. Too much can cause alkalinity to spike.
Effects of High Alkalinity
Allowing alkalinity to remain too high can lead to a number of detrimental effects:
Cloudy water
High total alkalinity causes carbonates to precipitate from the water, forming scale on hot tub surfaces and making the water appear cloudy.
Scale buildup
In addition to cloudiness, carbonate scale will form limescale deposits on the tub shell, plumbing, jets, and heater elements. This scales reduces heating efficiency. Acidic cleaners are required to remove it.
Difficulty adjusting pH
With a high buffering capacity from excess alkalinity, it becomes very difficult to lower the pH by adding acid. The alkalinity neutralizes the acid before it can lower the pH as desired.
Eye and skin irritation
Excessive alkalinity causes the water to have a high pH, which makes the water harsh and irritating for soakers. It can dry out skin and make eyes red and swollen.
Bather discomfort
The high pH environment feels slippery and causes most people to feel a tingling, itching sensation on their skin. Bathing time may be cut short due to discomfort.
Poor sanitizer efficiency
The high pH caused by high alkalinity reduces the effectiveness of chlorine and bromine sanitizers. More sanitizer needs to be added to reach ideal concentrations for killing germs at high pH.
Corrosion damage
High pH quickly corrodes metals components like handrails, pump impellers and heater coils. This leads to expensive repairs down the line.
Reduced filtration
Scale encrusted filters work less efficiently to trap particles and debris. More particles end up back in the water, making it dirtier.
Testing Alkalinity
To determine the current total alkalinity level, use either test strips or a digital tester:
Test strips
Dip the alkalinity test strip in a water sample for 1 second. Compare the resulting color to the color chart on the bottle to estimate the ppm.
Digital testers
Add water sample to a vial with pre-measured indicator powder. Cap vial and swirl until powder dissolves. Insert vial in tester and note ppm reading.
Test alkalinity weekly or each time you add more than a few bathers to the tub. Adjust as needed to maintain an ideal 80-120 ppm level.
How to Lower Alkalinity
Here are a few methods you can use to lower total alkalinity:
Partially drain the tub
Draining out 10-25% of the water volume and refilling will substantially reduce alkalinity. Be sure to refill with fresh water only.
Use an alkalinity decreaser
Chemicals such as sodium bisulfate will lower alkalinity when added in the correct dosage. Approximately 1.5 oz of decreaser drops alkalinity by 10 ppm in a 400 gallon tub.
Add acid
Muriatic acid or sodium bisulfate (pH decreaser) will lower both pH and alkalinity. However, take care not to lower pH below 7.2.
Run jets and add chlorine
The jets help circulate acidified chlorine through the water to lower alkalinity gradually. Add 1.5 oz chlorine to start.
Add baking soda
Counterintuitively, a small amount of sodium bicarbonate (baking soda) can lower carbonate alkalinity by converting carbonates to bicarbonates.
Prevention
To avoid having to deal with high alkalinity again:
– Test alkalinity weekly and adjust as needed.
– Change hot tub water every 3-4 months.
– Limit sodium bicarbonate or lithium bromide additions.
– Maintain an ideal pH of 7.2-7.6.
– Keep calcium hardness under control.
– Use an in-line scale inhibitor to reduce calcium carbonate precipitation.
Conclusion
High total alkalinity is problematic for hot tub water balance and comfort. Avoiding overuse of chemicals, changing the water regularly, and testing alkalinity often can help prevent it from climbing too high. If the alkalinity does creep up, there are several effective treatment options to bring levels back down into the ideal 80-120 ppm range again. With proper ongoing maintenance, you can keep alkalinity balanced and avoid many potential issues.