The quick and easy guide to balancing fresh hot tub water

This guide covers the straightforward steps you need to carry out to set up the water in your newly filled hot tub.

Draining and refilling is part of owning a hot tub. On average, your water needs to be changed roughly every three months. Once refilled with fresh water, it will need to be chemically balanced and sanitised ready for use.

Why do I need to set up my hot tub water?

Incorrectly balanced water can lead to several issues. Some of the problems include:

  • Scale forming
  • Cloudy water
  • Uncomfortable bathing
  • Ineffective sanitiser

Top Tips

  • Using a pre-filter on your hose when filling the hot tub can make the setup easier. It removes unwanted deposits such as rust, metal and other contaminants. It can also reduce the amount of start-up chemicals you need to use.
  • Run your hose for a couple of minutes before filling the hot tub to flush out any ‘old’ water that will have been sitting in the hosepipe.
  • Fill your hot tub through the filter compartment to reduce the chances of airlocks when restarting pumps.

The hot tub is full (but not heated), now what?

Red Spa 6008 hot tub filling up in Suffolk

The first thing we need to do is a test and adjust the total alkalinity level of the water. Why? Well, total alkalinity works as a buffer for your pH level and will keep your pH level stable. A correct pH level is essential for your sanitiser to works effectively. So it’s vital to get this right first.

Ideal range for total alkalinity between 80 to 120 ppm.

Using test strips to measure total alkalinity level in hot tub

If your total alkalinity level is reading too high, then you need to use pH- (Minus/Reducer) to bring down the reading. If the level is too low, then you need to use a Total Alkalinity Increaser to raise the level.

Note: pH- if used to reduce your total alkalinity level, but you’ll need to use larger doses than if you were using it to adjust your pH level. About 15 grams of pH- per 1000 litres of water will reduce your total alkalinity level by 10 – 20 ppm.

Why not try out our hot tub chemical calculator, just enter the volume of your hot tub and chemical reading, and it will tell you what you need to add.

Mix the chemicals in warm water first to dilute the granules, then tip evenly around the deepest part of the hot tub.

Total Hardness (Optional)
If your test strips or water testing kit shows the Calcium Hardness/Total Hardness, then look at the result of this. It should be between 175 and 275ppm (parts per million)

If it is above the OK range, then you risk scale forming and cloudy water. It is difficult to lower Calcium Hardness, so we suggest the use of a Scale Inhibitor as a precaution.

If it is below the OK range, then you can use a Calcium Hardness Increaser to bring this value up.

Finally, you need to bring up your sanitiser level, whether it be chlorine granules, tablets or bromine.

What about pH?

We don’t worry about this at this stage as this will change as the water heats up, so we won’t do anything with this until the water is at temperature.

And that’s all for now folks. Now just leave your hot tub to heat up.

Rinse and Repeat

Once your hot tub is at temperature, test again to see what your levels read. If they are OK, then pat yourself on the back for a job well done, otherwise concentrate on getting your total alkalinity level right first. Using the same method, test, adjust and test again. Then once this is correct, check your pH level and adjust accordingly using the appropriate pH adjuster chemicals.

Once your water is balanced, then it should remain relatively stable for the duration of your hot tub water, but keep an eye on it and adjust if necessary.

Let's look at an example

We carried out water setup on a Red Spa 6008, let us go through what we did, once filled we testing the water, and our results were:-
Temperature: 15°c
Total alkalinity: 250ppm
pH: 7.5pm
Chlorine: 0 ppm

So we need to adjust the total alkalinity and bring up the chlorine level. So using our hot tub calculator, we need to
– add 150g of pH Minus to adjust the total alkalinity.
– add 10 grams of chlorine granules to bring up the chlorine level to 5ppm.

Using pH minus to reduce total alkalinity

After these adjustments were made we tested again and got the following results:
Total alkalinity: 120ppm
pH: 6.8pm
Chlorine: 5 ppm

So this looked pretty good, we left the hot tub heating and re-tested once at temperature, the results were
Temperature: 37c
Total Alkalinity: 180ppm
pH: 8.4pm
Chlorine: 2 ppm

So our water balance wasn’t still quite right, so another 80g of pH- was added to the water. Which resulted in the following readings
Total Alkalinity: 150ppm
pH: 7.2pm
Chlorine: 2 ppm

So all good there, just a minor tweak to the chlorine level and we’re good to go.

It's not an exact science

The thing to remember with water care is that it’s not an exact science and it will vary from fill to fill.

Not got time to read? Here's a quick summary for those short on time

In a nutshell to balance your water for the first time you need to

  1. Fill the hot tub
  2. Test and make an initial adjustment to your total alkalinity.
  3. Raise the sanitiser level
  4. Allow to heat
  5. Test again – if the total alkalinity level isn’t correct, adjust again. If it is OK, then check the pH level and adjust.
  6. Repeat these tests and adjustments over the next few days until they have stabilised.

Quick amount measures
1 teaspoon chlorine granules = 5g
1 teaspoon of pH Minus = 7g

A teaspoon of chlorine | The Tub Company | Suffolk

We hope you found this guide useful and has simplified starting your hot tub with fresh water. 

Of course if we have missed anything out or you have any questions regarding this guide please get in touch.

Happy Hot Tubbin’