Over the years, I’ve used several different methods for lowering the pH in my hot tub. I’m going to share with you the most effective ways and how to lower the pH step by step.
In order to lower the pH of hot tub water, you’ll need to add acid. The most popular choices are sodium bisulfate (dry acid) and muriatic acid (liquid acid), which are more commonly referred to as pH decreaser. Alternatively, white vinegar may also be used to lower the pH naturally without using chemicals.
In this article, you’ll learn:
- How to use acid to lower pH
- Pros and cons of each acid
- Why your pH is high
- How to prevent high pH in the future
How to lower the pH in your hot tub
You should always adjust the alkalinity first before making adjustments to the pH. A proper alkalinity level between 80-100 ppm buffers pH, preventing fluctuations in the pH. If the total alkalinity is too low, you won’t be able to keep the pH levels between the ideal range of 7.4-7.6.
Sodium bisulfate (dry acid)
One of the most common ways homeowners lower the pH in their hot tub is by using pH decreaser, also known as pH reducer or pH minus. The product contains sodium bisulfate, which is a dry acid available in granular form.
What you’ll need:
- Liquid test kit
(or test strips) - pH decreaser
- Gloves
- Goggles
- Bucket
- Wooden or plastic stirrer
How to lower pH using sodium bisulfate:
- Use a test kit to test and adjust the alkalinity to obtain a reading of 80-100 ppm.
- Use a liquid test kit (most accurate) or test strips (less accurate) to take a reading of the current pH level.
- Use these reusable chemical-resistant gloves and safety goggles to protect your eyes and skin when handling sodium bisulfate.
- Follow the instructions on the bottle to calculate the required dosage of pH decreaser to lower the pH to between 7.4 and 7.6.
- Half fill a large, clean bucket with fresh water and pour in the required amount of sodium bisulfate. Mix the granules with a wooden stirrer until completely dissolved.
- Turn on the pump and jets and pour the solution into the hot tub. Allow it to circulate for three to six hours with the cover off.
- Retest and make adjustments if necessary.
When sodium bisulfate is added to water, it increases the hydrogen concentration, which lowers the pH and total alkalinity. Although care needs to be taken when using any type of acid, sodium bisulfate in granular form is user-friendly.
It’s less caustic than liquid acid products, meaning that it will not damage surfaces as easily if it’s accidentally spilled. It’s also more practical as it can be stored in a wider range of conditions. Remember, dry acid is a lot safer than liquid acid, but you still need to exercise caution when handling it.
Muriatic acid
Liquid muriatic acid (or Hydrochloric acid) is cheaper and more effective than dry acid products, which is why it’s the most popular way of lowering pH levels in commercial settings.
There are many risks involved when using muriatic acid. You should only handle muriatic acid if you feel completely comfortable in your ability to do so.
What you’ll need:
- Liquid test kit (or test strips)
- Muriatic acid or Acid Magic
- Gloves
- Goggles
- Mask
- Apron
- Bucket
- Wooden or plastic stirrer
How to lower pH using muriatic acid:
- Use a test kit to test and adjust the alkalinity to obtain a reading of 80-100 ppm.
- Use a liquid test kit (most accurate) or test strips (less accurate) to take a reading of the current pH level.
- Put on your protective gear: long-sleeve gloves, safety goggles, chemical mask, and vinyl apron.
- Consult the instructions to determine the amount of muriatic acid you’ll need to lower the pH to between 7.4 and 7.6.
- In a large, clean, plastic bucket, dilute one part acid into 10 parts of water. Always add the acid to the water, not the other way around. Mix the solution thoroughly using a wooden stirrer.
- Carefully, pour the solution into the hot tub and run the jets to aerate it. Allow the acid to circulate overnight with the cover on.
- Retest the pH and adjust if necessary.
With a pH level of 1.0, muriatic acid is a million times more acidic than water. It’s highly corrosive, which is why it’s necessary to dilute it before adding it to your spa water. This powerful acid can easily burn through flesh, metal, and concrete.
A safer alternative is to use a muriatic acid replacement product called Acid Magic. It has the pH reduction properties of muriatic acid but is less caustic and gives off 90 percent fewer fumes.
The manufacturer states that it will not cause burns to the skin, but it’s still advisable to wear full protective gear when handling Acid Magic.
Vinegar
If you want to reduce the number of chemicals you use in your spa, then using vinegar is a safe and natural way to reduce the pH.
What you’ll need:
How to lower pH using vinegar:
- Use a test kit to test and adjust the alkalinity to obtain a reading of 80-100 ppm.
- Use a liquid test kit (most accurate) or test strips (less accurate) to take a reading of the current pH level.
- Measure four cups (1 liter) of white vinegar and pour it directly into the middle of your spa.
- Run the pump and jets to allow the vinegar to circulate for at least two hours with the cover removed.
- Retest the pH levels. If necessary, add more vinegar in four-cup increments until you reach a reading between 7.4 and 7.6.
While it’s perfectly possible to reduce the pH using vinegar, it isn’t a very practical method for a number of reasons. Firstly, vinegar adds acetates to the water, which creates a secondary buffer system that isn’t desirable. Secondly, vinegar is a relatively weak acid, meaning that you have large quantities that can result in a foul-smelling odor.
See my article for more information on the practicalities of using vinegar to reduce pH. Vinegar will only save you a few dollars over the course of a year, and sodium bisulfate is far more effective and less hard work.
Why is the pH high?
Very high total alkalinity is the primary reason for high pH levels. The minerals in hard water act as a buffer that reduces the amount of acid, resulting in a high pH. Another cause is the combination of bubbles and high water temperatures in hot tubs that create carbon dioxide gas, which raises the pH.
If you live in an area with hard water or you use a well, it’s likely to have a higher-than-normal pH level. Adding shock to the water can also cause a temporary spike in the pH as it breaks up the chloramines in the water. It may also be that you accidentally added too much pH increaser to the water when making your weekly adjustments.
The fact that hot tubs naturally produce carbon dioxide, which raises pH, is why you need to be proactive when it comes to maintaining the water chemistry, even if the hot tub isn’t being used. You must act quickly to balance the water as high pH can cause cloudy water, calcium and scale build-up, and damage to the filter and plumbing.
Never use your hot tub if the pH is high as you may experience itchy skin and burning eyes.
How to prevent high pH
You should never have to chase the pH levels around in your spa. If you’ve found yourself doing so, then it’s best to drain all of the water and start afresh.
Remove biofilm
Before draining your hot tub water, use this Ahh-Some line flush to get rid of any harmful biofilm hiding in the plumbing. If you’ve never used line flush, check out this guide to removing biofilm and the importance of doing so.
After you’ve drained the water, you’ll need to use this surface cleaner to disinfect the empty spa shell before you fill up again.
Hose filter
Most hot tub owners fill up their spa using an outside garden hose. Unless you live in an area with extremely soft water, you should have a pre-filter attached to your hose.
Inline pre-filters are inexpensive and highly effective, removing up to 98 percent of metals and other contaminants from the water. This means that the water in your spa is a lot fresher and requires fewer chemicals to balance the water.
Metal sequestrant
For those living in hard water areas or who source their water from private water wells, it’s worth adding metal sequestrant to the water. A metal sequestrant binds dissolved metals, such as copper and iron, in the water so that they can be removed by the filter.
This stops a build-up from occurring and prevents the metals from settling on the spa’s surface, which can cause staining. If you suspect your water may contain high levels of dissolved metals, use these special metal test strips to test the levels of metals in the water.
