There are a few different products that can be used to lower alkalinity in a hot tub:
pH Down
pH Down, also known as sodium bisulfate, is one of the most common products used to lower alkalinity in hot tubs. It lowers both pH and alkalinity at the same time. pH Down comes in either a dry or liquid form and is added directly to the hot tub water. It works quickly to bring down alkalinity levels.
How pH Down Works
Sodium bisulfate reacts with the bicarbonate ions in the water to lower both pH and alkalinity. Each pound of pH Down added to a hot tub will lower alkalinity by around 10 ppm. It’s important not to add too much at once, as lowering alkalinity too quickly can shock the water. pH Down should be added gradually and levels tested frequently.
Benefits of pH Down
- Lowers both pH and alkalinity
- Cost effective
- Works quickly
- Readily available
Potential Drawbacks
- Can lower pH too much if overused
- Requires frequent testing to monitor levels
- Can cause corrosion issues if pH is too low
Muriatic Acid
Muriatic acid, also known as hydrochloric acid, can also be used to lower alkalinity and pH levels in hot tubs. It is a stronger acid than sodium bisulfate. Muriatic acid comes as a liquid and must be diluted before adding to the tub.
How Muriatic Acid Works
When diluted with water and added to the hot tub, muriatic acid reacts with the bicarbonate ions, converting them into carbon dioxide gas which escapes from the water. This lowers alkalinity. Muriatic acid also lowers pH at the same time.
Benefits of Muriatic Acid
- Lowers alkalinity and pH quickly
- Concentrated formula is effective in small doses
- Inexpensive
Potential Drawbacks
- Can cause damage if not diluted properly
- Lower pH too much if overused
- Very acidic and requires safe handling
Alkalinity Down
Alkalinity down, also called sodium bisulfite, is designed to lower alkalinity specifically without affecting pH. It comes as a granular product that dissolves when added to the hot tub water.
How Alkalinity Down Works
Sodium bisulfite works by reacting with bicarbonates in the water to lower alkalinity levels without impacting pH. It is slower acting than pH down but may be preferable if only alkalinity needs to be reduced.
Benefits of Alkalinity Down
- Targets alkalinity specifically
- Won’t affect pH levels
- Adds sodium which can help soften water
Potential Drawbacks
- Acts slowly compared to muriatic acid or pH down
- Requires very precise dosing
- Relatively expensive
Acid Washing
Acid washing with muriatic or sulfamic acid can also be used to lower alkalinity in a hot tub. This involves draining the tub, scrubbing the empty shell, then refilling and balancing the water.
How Acid Washing Works
Cleaning the empty hot tub shell with an acidic solution dissolves scale, calcium deposits, and other buildup that may be contributing to high alkalinity. Once dissolved, these deposits are rinsed away. Refilling with fresh water resets alkalinity and pH to lower levels.
Benefits of Acid Washing
- Also removes scale and mineral deposits
- Resets alkalinity and pH completely
- Improves circulation
Potential Drawbacks
- Labor intensive process
- Requires draining and refilling hot tub
- Doesn’t work for ongoing alkalinity issues
Conclusion
There are several effective options for lowering alkalinity in hot tubs. pH Down (sodium bisulfate) is the most commonly used for its availability and ease of use. Muriatic acid and specialty alkalinity down products can also be used for quicker reduction or to target alkalinity specifically. For a thorough reset, acid washing is an option but requires draining and refilling the tub. Any of these methods can help bring high alkalinity back down to the 80-120 ppm range recommended for hot tub water balance.