Hot Tub Alkalinity Guide

If your hot tub’s Total Alkalinity (TA) isn’t within a certain range, the sanitiser you add to it won’t work properly. 

Pretty soon, bacteria will take over your spa and it won’t be safe to use.

Luckily, keeping on top of your hot tub’s Total Alkalinity isn’t hard. You just need to know what you’re looking out for and how to get it back in balance.

Read on to find out everything a hot tub owner needs to know about Total Alkalinity.   

What is Total Alkalinity?

Your hot tub’s Total Alkalinity is the amount of dissolved alkaline compounds – like bicarbonate, carbonate, and hydroxide – in its water. 

These compounds attract and release Hydrogen ions, which neutralise acid in your spa’s water and increase its pH level.

Why is your hot tub’s Total Alkalinity important?

If your spa’s TA is out of whack, the sanitiser you add to your hot tub won’t work properly. This will allow bacteria to flourish and quickly make your hot tub unsanitary and unsafe to use.

If your spa’s Total Alkalinity is too low, its water will be too acidic. Alongside preventing your sanitiser from working, acidic hot tub water will also:

• Irritate your eyes and skin.
• Corrode and permanently stain your spa’s components.
• Make your pH levels impossible to raise to the right level.

If your spa’s Total Alkalinity is too high, its water will be too alkaline. As well as stopping your sanitiser from killing bacteria as effectively as possible, alkaline spa water will also:

• Cause limescale to build up on your spa’s components, damaging electronics like pumps and heaters and blocking pipes.
• Turn cloudy, milky, or foamy.
• Send your pH levels through the roof and make them impossible to lower.

How Total Alkalinity affects your hot tub’s pH levels

Your hot tub’s Total Alkalinity and pH levels are both closely linked. Each time you change one, the other is affected as well.

pH is measured on a scale from zero (acidic) to fourteen (alkaline), with seven being neutral. Your hot tub’s water needs to be between 7.2 and 7.6 pH at all times. 

If your spa’s TA is too high, it’s pH levels will be sky high and just about impossible to keep below 7.6. If it’s too low, the water will be far too acidic and difficult to bring up to 7.2.

When you’re adjusting your hot tub’s chemicals, you should always get the TA dialed in first, then adjust the pH. If the TA isn’t within the right bounds there’s no chance the pH will stay stable.

What’s the right amount of Alkalinity?

Your hot tub’s Total Alkalinity needs to be between 125 and 155 parts per-million (PPM).

You should test your hot tub’s TA once a week. If it’s below 125 PPM, you can increase it with an alkalinity increaser. If it’s above 155 PPM, you can decrease it with a pH decreaser, as decreasing the water’s pH will lower its alkaline concentration.

What causes high alkalinity in a hot tub?

Your spa’s TA tends to be increased by:

• Contaminants like suntan lotion and make-up washing off when you go for a dip.
• Hard water, which has a high pH.
• Going overboard with high pH hot tub chemicals like spa shock.

Measuring your spa’s Total Alkalinity once a week will help you catch a significant increase before it becomes a problem.

What causes low alkalinity in a hot tub?

Your spa’s TA is generally increased by:

• Rainwater diluting your hot tub’s water.
• Sweat that runs off you during a soak.
• Being heavy handed with low pH home spa chemicals like chlorine tablets.

Testing your hot tub’s Total Alkalinity each week will help you catch a serious dip before it starts causing headaches.

How to adjust your hot tub’s Total Alkalinity

To adjust your spa’s TA level, you’ll need:

1. A hot tub test strip or liquid test strip.
2. Alkalinity increaser to raise your hot tub’s Total Alkalinity.
3. pH decreaser to reduce your hot tub’s Total Alkalinity and pH level.
4. pH increaser to raise your hot tub’s pH level after you’ve adjusted its Total Alkalinity. 

Once a week, test your hot tub’s TA with a test strip or a liquid test kit: 

• If it’s between 125 and 155 PPM you can move straight on to adjusting the pH.
• If it’s below 125 PPM, grab your alkalinity increaser.
• If it’s above 155 PPM, grab your pH decreaser.

Keep your hot tub running at this point to help mix the chemicals you add into the water. But close your hot tub’s air valves so the jets aren’t running too powerfully so the chemicals don’t evaporate too quickly.

Refer to the manufacturers’ instructions to see how much alkalinity increaser or pH decreaser you’re going to need to add to your spa to get the TA right.

Be sure to carefully measure out the chemical you need before adding it, as you need to be precise to get the right results.

Once you’ve added the alkalinity increaser or pH decreaser, test your hot tub’s water again. If the TA still isn’t within 125 and 155 PPM, adjust until it is.

Once your spa’s Total Alkalinity is in balance, test its pH and then use pH increaser or decreaser to get that within 7.2 and 7.6.

Before you get in your hot tub, test its TA and pH levels again to make sure they’re where they need to be and adjust again if necessary.

Summing up

And that’s all there is to it.

Test your spa’s Total Alkalinity once a week as part of your hot tub maintenance routine, add a few scoops of chemicals if they’re needed, and then finish off by adjusting the pH.

And if you ever need to troubleshoot, just refer back to this guide to remind yourself of everything you need to know about Total Alkalinity.

And for more hot tub maintenance tips – plus our pick of the best hot tubs on the market today for every budget – pick up your free copy of the latest edition of WhatSpa? magazine.

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