How to Increase Alkalinity in Hot Tubs

Maintaining proper water balance is essential for the health and enjoyment of your hot tub. One crucial aspect of water chemistry is alkalinity, which is key in stabilising pH levels and preventing fluctuations. 

In this guide, we’ll explore the importance of alkalinity in hot tubs, the effects of low alkalinity, signs of imbalance, and steps to increase alkalinity for a pristine hot tub experience with hot tub water balancers

A blue hot tub in a garden















Hot Tub pH Levels Explained

pH levels measure the acidity or alkalinity of water on a scale from 0 to 14, with 7 being neutral. The ideal pH range for hot tubs is typically between 7.2 to 7.8, slightly alkaline to ensure comfort and equipment longevity. 

Guide to pH levels in hot tubs

The Effects of Low Alkanility in a Hot Tub

If your hot tub has low alkalinity, this can lead to pH instability, causing fluctuations that result in water that is too acidic. This imbalance can corrode metal components, damage equipment, irritate skin and eyes, and reduce the effectiveness of hot tub sanitisers

Signs of Low Alkalinity in Hot Tubs

  • pH levels are consistently below 7.2.
  • Rapid pH fluctuations despite pH adjustments.
  • Corrosion or straining on metal surfaces.
  • Cloudy or foamy water.
  • Skin and eye irritation after soaking. 

Steps to Increase Alkanity in Hot Tubs

Maintaining proper water balance is critical for a smooth and comfortable hot tub experience. So, how do you increase the pH of your hot tub water? Our step-by-step guide explains how to raise your hot tub’s alkalinity.

1. Test Your Hot Tub’s Water

Firstly, you want to test your water's pH and total alkalinity levels. We recommend using pH and total alkalinity test strips or a digital pH meter for an accurate test. Make sure to turn off all jets before testing the water.  

If using a pH strip, dip it into the hot tub water for 2 seconds, then remove it and wait for around 10 seconds. Compare the colour change of the strip with the pH colour chart to determine the pH level. 

hot tub water testing

2. Add an Alkalinity Increaser

If the pH level is too low or too acidic, you should add an alkalinity increaser containing sodium carbonate (soda ash) to increase it. The solution should be added to your hot tub at a rate of 50g per 4,545 litres (1000 gallons) of water. We suggest adding the alkalinity increaser carefully and slowly so you don’t make the mistake of adding too much. You can always add less, wait, test, and then add more if needed. 

Hot Tub Water Volume (Gallons)

Amount of Soda Ash to Use (Grams)

200 Gallons (909 litres)

10 g

400 Gallons (1,818 litres)

20 g

600 Gallons (2,728 litres)

30 g

800 Gallons (3,637 litres)

40 g

1000 Gallons (4,545 litres)

50 g

Follow our hot tub water volume to alkalinity chart below to ensure you add the right amount. We also recommend checking the manufacturer’s instructions. 

A grey hot tub on a balcony

3. Turn on Hot Tub Pumps

Once you’ve added the soda ash to the hot tub water, turn on the pumps whilst keeping the air valves closed to allow the water to circulate for 2-3 hours. 

4. Turn off the Pumps

After 2-3 hours, turn off the hot tub pumps and let the water settle. 

5. Re-test the pH Level of the Hot Tub

Once settled, re-test the pH level to check the alkalinity levels are in the correct range, between 7.2 and 7.8. The alkalinity should fall between 80ppm to 120ppm. 

If your hot tub pH levels are still slightly low, repeat the process by adding a little more alkalinity increaser. 

What if the Hot Tub pH is too high?

On the other hand, if the pH level of your hot tub’s water is too high, you need to reduce its total alkalinity by adding a pH reducer containing sodium bisulphate, also known as dry acid. 

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Check out the rest of our blog guides and product recommendations to help you maintain your hot tub.