Will baking soda lower alkalinity in a hot tub?

Maintaining proper water chemistry is crucial for keeping a hot tub safe and enjoyable to use. The three most important water balance factors are pH, alkalinity, and calcium hardness. pH determines whether the water is acidic or basic. Alkalinity acts as a buffer to prevent fluctuations in pH. Calcium hardness relates to the mineral content in the water. Getting these levels right goes a long way toward preventing problems like corrosion, cloudy water, scale buildup, and skin/eye irritation.

One common question hot tub owners have is whether adding baking soda can lower total alkalinity. Baking soda (sodium bicarbonate) is a popular product used to increase pH and alkalinity. However, there are scenarios where alkalinity is too high, so people wonder if baking soda will actually lower levels if they are off. Understanding the science behind how baking soda reacts in water is key to answering this question.

How Baking Soda Affects Alkalinity

Alkalinity is a measure of the capability of water to resist changes in pH. It refers primarily to the concentration of carbonate, bicarbonate, and hydroxide ions in the water. When alkalinity is high, it acts as a buffer against rapid shifts in pH when acids are added. Conversely, when alkalinity is low, the pH will fluctuate dramatically with even small additions of acids or bases.

The target alkalinity range for most hot tubs is 80-120 parts per million (ppm). Maintaining levels in this range helps to keep the pH stable between 7.2-7.8. If the alkalinity drops below 80 ppm, the pH will be prone to bouncing around. Above 120 ppm, and the water will have too much resistance to pH change.

So how does baking soda fit into the picture with alkalinity? Sodium bicarbonatedissociates into sodium (Na+) and bicarbonate (HCO3-) ions when dissolved in water. Bicarbonate is one of the key ions that contributes to total alkalinity. Adding baking soda directly increases the concentration of bicarbonate in the water, thus raising the overall alkalinity.

This is why baking soda can be used to boost alkalinity levels if they are too low. However, it does not work the other way around. Adding excess baking soda cannot reduce high alkalinity on its own. The bicarbonate ions will stay dissolved in the water, continuing to contribute to total alkalinity. To lower alkalinity, other chemicals like sodium bisulfate or muriatic acid are needed to actively remove bicarbonate ions.

Other Ways Baking Soda Affects Hot Tub Water Chemistry

In addition to increasing alkalinity, baking soda also raises the pH and calcium hardness of hot tub water:

– pH – When sodium bicarbonate dissociates, it forms sodium hydroxide. This hydroxide compound is alkaline and will directly cause the pH to climb.

– Calcium Hardness – Most baking soda products contain traces of calcium carbonate as well. Calcium from the calcium carbonate dissociates in water and leads to higher calcium hardness.

While baking soda contains properties to raise pH, alkalinity, and calcium hardness, it does not have any mechanisms to directly decrease these levels if they are already elevated. Adding more baking soda to water with high mineral concentrations will only spike the parameters further.

How to Actually Lower Total Alkalinity

If test results show total alkalinity over 120 ppm in a hot tub, bringing it back down requires using different chemicals. Here are two options:

Sodium Bisulfate

Sodium bisulfate (also called dry acid) lowers alkalinity in a hot tub by directly reducing the concentration of bicarbonate and carbonate ions when dissolved. It works quicker than muriatic acid but may cause a rapid drop in pH as well.

To lower alkalinity with sodium bisulfate:

1. Test the current alkalinity level with an accurate test kit.
2. Determine the amount of sodium bisulfate needed to reduce alkalinity by 20-30 ppm based on the chemical’s instructions.
3. Evenly dissolve the needed amount of sodium bisulfate in a cup of hot water first.
4. Add the dissolved sodium bisulfate to the hot tub water while running the jets and hot tub cover open.
5. Test alkalinity again after several hours once fully circulated.
6. Repeat steps to continue lowering in 20-30 ppm increments as needed until target range is reached.

Muriatic Acid

Muriatic acid is a diluted hydrochloric acid solution. It lowers alkalinity and pH by removing bicarbonate, hydroxide, and carbonate ions from the water. Muriatic acid works slower than sodium bisulfate but gives more gradual results.

Follow a similar dosage and testing process as above if using muriatic acid to reduce alkalinity:

1. Test current alkalinity level.
2. Calculate amount of muriatic acid needed to reduce by 20-30 ppm.
3. Slowly add acid directly to hot tub over an access point like filter while running jets.
4. Test alkalinity after several hours once fully circulated.
5. Repeat to lower to target range in increments.

Always handle muriatic acid with great care by wearing gloves and avoiding fumes. Never add chemicals directly to the hot tub while bathers are still soaking. Confirm the pH and adjust as needed after lowering alkalinity.

Preventing Alkalinity Imbalances

While baking soda alone will not reduce elevated alkalinity, taking some preventative steps can help avoid major spikes and keep levels in balance:

• Monitor alkalinity, pH, and calcium hardness each time before adding any chemicals.
• Make gradual alkalinity adjustments of no more than 30 ppm up or down.
• Use sodium bisulfate instead of muriatic acid if lowering alkalinity to avoid pH swings.
• Limit the number of bathers and frequency of use to reduce chemical demand.
• Replace hot tub water regularly per the manufacturer’s recommendations.
• Shock and clean filters when needed to prevent scale contributing to high alkalinity.
• Consider using a mineral purification system to naturally supplement chemical balance.

Following the proper start-up procedure and maintaining an optimal sanitizer level (chlorine 2-5 ppm or bromine 3-5 ppm) also provides added stability to the other water parameters.

Conclusion

Baking soda will readily increase alkalinity in a low range hot tub when added. However, baking soda alone does not decrease elevated alkalinity levels. Adding more baking soda to water with high alkalinity only spikes it higher. To actually reduce total alkalinity, sodium bisulfate or muriatic acid should be carefully dosed based on test readings. Preventing major alkalinity fluctuations through regular water care and replacement is a better approach than relying on chemicals to adjust high ranges down after the fact. Maintaining balanced water chemistry takes diligence, but is essential for a safe and relaxing hot tub experience.