How To Raise Alkalinity In Your Hot Tub (2 Easy Methods)



Total alkalinity (TA) is a buffer for your hot tub’s pH level, allowing it to resist wild fluctuations in the water chemistry.

Like swimming pools, the ideal range for alkalinity in your spa or hot tub is between 80 and 120 parts per million. Any higher or lower and you will start to see some unwanted side effects in your water.

Let’s talk about why alkalinity drops, why it’s important to maintain at the right level, and the right ways to raise alkalinity in your hot tub.

Why You Have Low Alkalinity

As total alkalinity helps to stabilize the tub’s pH level, when one drops, so does the other. If pH becomes low, the TA level drifts to the lower end of the scale as well.

What causes this dip in pH and alkalinity? 

First, it can be caused by humans. The majority of hot tubs are heavily trafficked, and people bring in tons of pollutants that can alter the water chemistry. This can be anything from body oil and sweat, to chemical residue from your bathing suit, and even urine.

Another reason might be from Mother Nature herself. Rain water is a common offender in lowering the alkalinity of water, as it leans on the acidic side of the pH scale. If you don’t use a hot tub cover, you may find your water out of balance after a downpour.

Chlorine could also be the culprit. Using chlorine tablets in the tub can bring down the alkalinity, as these tablets have a low pH level. 

Why Low Alkalinity Is Bad News

Hot tub alkalinity must measure above 80 ppm. If it doesn’t, the following issues will start to take hold of the tub:

  • Green tub. When hot tub water turns green, it’s a pretty strong indication you have a problem on your hands. However algae can’t grow in a neutrally balanced environment. When the alkalinity (and thus the pH) drops, algae blooms are almost inevitable.
  • Corrosion. While the majority of tubs are made from fiberglass, low alkalinity water can still cause corrosion issues. This can occur on any metal surfaces that may be in the tub, or inside equipment like the pump and filter. If eroded, they’ll likely have to be fully replaced which can cost a pretty penny.
  • pH will fluctuate. With not enough alkalinity in the water, this will cause the pH level to fluctuate wildly. One minute you may have an acidic tub, the next, an alkaline one. This is also referred to as pH bounce, and it happens when there isn’t enough pH buffer present in the water.
  • Irritation to bathers. Low alkalinity water turns it acidic, and this will irritate the people in the tub. I’m not talking about it being a nuisance, but rather, it will literally irritate them via their eyes, skin, and nasal passages. For some people it can even cause respiratory distress.
  • Damage to the tub. Depending on the tub’s material, staining, etching, delamination, and cracking are all possible outcomes when low alkalinity is present. A vinyl cover can also be damaged, becoming stiff and brittle over time.

How To Raise Total Alkalinity In A Hot Tub

With so many detrimental effects from low alkalinity, you can appreciate how important it is to restore it to its proper level. 

You can raise the tub’s TA using the following methods:

Method #1: Use Baking Soda

Baking soda (sodium bicarbonate) is an extremely common way to raise alkalinity in a hot tub. In fact, it’s so common that products such as Alkalinity Increaser or Alkalinity Up are basically baking soda in a fancy bottle.

Using baking soda ensures you’re working with an extremely safe chemical. Not only is it easy to handle, but it can be poured directly into the tub, and you can find it at any grocery store. 

In addition, you’ll be paying a lot less for generic baking soda compared to shelling out for a product like Alkalinity Up.

The nice thing about using baking soda is that it raises the water’s alkalinity level while having a minimal effect on the pH level.

Here’s how to add it to your hot tub:

  1. Start by testing your water’s alkalinity level. You can do this using test strips, a liquid testing kit, or a digital tester. Once you have this level, calculate how much you need to raise the alkalinity to at least 80 ppm.
  2. Measure out the dosage of baking soda your tub requires. As a general rule, use 1 tablespoon of baking soda per 100 gallons of water. So if you have a 600 gallon tub, use 6 tablespoons. Unfortunately this won’t give you a set increase in ppm, so you’ll have to do some trial and error balancing.
  3. Suit up in rubber gloves and goggles, as you don’t want baking soda stinging your eyes.
  4. Add the baking soda to a bucket of water to dilute it. Stir it up until it’s fully dissolved.
  5. Pour the solution into the tub, and wait 6 hours for it to be fully circulated.
  6. Retest the water and adjust accordingly.

Method #2: Use Soda Ash

Soda ash (sodium carbonate) can also be used to raise alkalinity in a hot tub.

The main difference when using soda ash is that it dramatically raises both the TA and pH level of the water, whereas baking soda is a bit more conservative. This can cause an issue if your pH doesn’t need much altering to begin with.

Here’s how to add it to your hot tub:

  1. As usual, start by testing your hot tub water to get the current TA level. You can use test strips, a liquid kit, or a digital tester for this.
  2. Like baking soda, soda ash should be measured out in tablespoons, with 1 tablespoon per 100 gallons of water.
  3. Put on your safety gear – rubber gloves and protective eyewear.
  4. Dilute the soda ash by adding it to a bucket of water. Stir it up using a wooden stir stick until the chemical is fully dissolved.
  5. Pour the solution into the hot tub.
  6. Wait a few hours so the hot tub’s system can fully circulate it.
  7. Retest the water and make any necessary adjustments.

How To Bring Your pH Back Down

Sometimes water balancing doesn’t go quite as planned, and there could be times where you’ll end up with a high pH after raising alkalinity (more common if you’re using soda ash).

Not to worry, you can bring this back down using an acid – either muriatic acid or sodium bisulfate. Sulfuric acid is another option, but as it significantly adds to the TDS level in the water, it’s rarely used.

Sodium bisulfate is a dry acid, and the safer of the two to work with, although it can be dangerous if not handled properly. 

Muriatic acid is highly corrosive. You need to take great care when working with it to avoid accidents that could land you in the ER. It’s also the cheaper option, which is why it’s the more commonly used method.

Pick Your Poison!

Either baking soda or soda ash will raise alkalinity in a hot tub. 

You can’t go wrong with either, but it’s generally accepted that baking soda is the best method to use.

This is because it minimally affects the pH level of the water, whereas soda ash can dramatically spike the pH, resulting in more time spent balancing the water.

Categories: Hot Tub Care, Hot Tub Chemistry