Hot Tub Chemical Guide

Here is our sunset spas hot tub chemical guide written to help and advise on how to keep your hot tub running safely and without any problems!


1)      Which Sanitiser should I use in my hot tub?

So this is a question we hear a lot, and the 3 main and most popular options are

  • Chlorine
  • Bromine
  • Silver Based Liquid


Chlorine is the most popular sanitizer it’s a very strong chemical and fast reacting so its dissolves quickly once in the water. It’s the cheapest hot tub and pool disinfectant to use but some users have problems with the smell, skin reactions and eye irritation. Chlorine comes in tablet or granular form. Levels should be maintained at 3-5ppm.


Bromine is an alternative to chlorine however does contain a small amount of chlorine, it’s less harsh than chlorine and doesn’t smell as potent as chlorine, and it’s also slower reacting so takes more time to dissolve into the water, hot tub users typically tend to switch to bromine if they are having negative reactions to chlorine. Bromine is more effective at all ph ranges than chlorine. Levels should be maintained at 4-6ppm. Bromine comes in tablet or granular form.


Silver based products; such as aquafinesse. These are a weekly dosage alternative that also typically works with a non-chlorine shock product. These products are usually quite expensive £70-£90 for a 2-3 months treatment, but are easy to use with just a weekly dosage, ph levels should still be maintained at 7.2 -7.8 if not, your ph level may be very low or very high and your hot tub is at risk of getting damaged! They are very soft on the skin and this is the main reason why they are used.



If I choose Chlorine/Bromine, should I go for tablets or granules?


Tablets are good to use as they slowly release the chlorine/bromine into the water which is ideal if you only use your hot tub 1-3 times a week. You put the tablets in a dispenser and to start off with, you’re going to want to test the sanitizer level every couple of days, after a couple of weeks you should know how many tablets will keep your hot tub water with the correct level and you can test less often. If you plan to use it more than 1-3 times a week then the tablets will struggle to release enough chlorine/bromine to keep it at the desired level.


Granules are more effective to use if you use your hot tub from 3-7 times a week. Simply premix around 10-15g of granules into hot water and pour this in immediately  after you use the spa, this will get rid of any dirt just bought in and will keep it clean for the next use. By premixing the granules in hot water and then pouring it into the hot tub water the granules are immediately in the hot tub water compared to the slowly dissolving tablets.


3)      Test Strips

Depending on which sanitizer you have chosen you will need the specific test strips for that sanitizer. Hot tub test strips typically test for, chlorine/bromine, ph and total alkalinity.

To use these, simply dip them gently in the water and hold it there for around 2-5 seconds, then bring them up and hold the strip horizontally, this will ensure the colours don’t mix together and give an inaccurate result. Compare the strip to the colour chart and you can compare if your levels need increasing or decreasing.


Note Total alkalinity ensures that your ph level will stay stable and not move on its own, you can adjust the Total Alkalinity (referred to as TA) by using ta+ to increase it, but there is not a ta- product to decrease it, to decrease it you have to use ph -, which can make things unnecessarily complicated, we recommend you get your ph level correct and forget about the Total alkalinity level as it will most often go to the desired level.


4)      PH


The Ph level you want your hot tub to have is 7.2 – 7.8, though keeping it at the lower end is ideal so 7.2 – 7.4 is the desired level.


Here’s a Table of the effects of having imbalanced ph


High PH

Low PH

Scale – Damage Heater, Pumps And Jets

Acidic Water

Cloudy Water

Metal Parts Will Corrode

Chalky Residue on Shell

Sore Eyes + Effects Of Sitting In Acid Water?


So you now know why you want to keep the PH at the correct level, and to do this it’s very simple, the 2 products you need are simply called PH + and PH -, PH plus increases the ph level and PH minus Decreases it.

So when adjusting your level you want to use a small amount at a time and this just makes it easier as you don’t want to be juggling the level. You want to slowly bring it to the correct level and to do this just simply use 10g at a time, then wait 4-5 hours and retest the levels and then repeat if you have to.


The PH level will stay generally stay at the level once you have adjusted it but you need to be awatr of a few things as to why it could change:


1)      Chlorine has a PH level of 7

2)      Bromine has a PH level of around 5

3)      Topping up the water will change the PH closer to your tap water PH

4)      Body oils, fragrances and moisturises will change the PH



5)      Hard water



A lot of areas in the UK are hard water which means they have a high calcium level this can also lead to scale in your hot tub which will damage your heater, pumps and jets!

You can fill your hot tub with a water softener and this will greatly reduce your calcium levels in the water and stop any problems from occurring, these can however cost up to £300 or use a product called “Spa scale remover” which is a liquid product that is used weekly to remove and stop scale formation.



6)      Foamy water

Foaming and scum formation are serious detractions from the goal of crystal clear spa and hot tub water. Spa chemicals generally do not cause foaming. The most common cause is the reaction of body oils and cosmetic residues with the natural alkalinity of the water. This can lead to the formation of "soaps" and the possibility of a foamy water problem. Using the product “Foam Away”, simply spray a small amount of it on the foam and within a few minutes the foam will disappear into the filter.


7)   Cloudy Water


So you may have found you have used the hot tub excessively for a massive party one night and that the next morning you check the tub and it’s cloudy and looks like your favourite soup. Well, you’re thinking the chlorine level was right before you used it,  but then again the beer and the 7 different people in there probably didn’t help! Well this is where Non Chlorine Shock is used - we recommend using it when and if your hot tub water turns cloudy, but most chemical companies try to push it as a once a week thing, we recommend this only if you continually have cloudy water problems. To use this simply premix around 20-25g of Non Chlorine Shock and then add to the spa water, you can use the spa 1-2 hours after it has been added.


8)   Filter Cleaner

Cleaning your hot tub filter is very important to ensure the water stays clean and the hot tub water is flowing through the system correctly. You should clean your hot tub filters once every 2 weeks with your normal garden hose, to get rid of any big bits of dirt. Then use a Filter cleaner chemical to thoroughly get rid of oils and fats that can clog the pleats up thus reducing flow, approximately every 1-2 months. This will make ensure the filter lasts as long as possible. It is also a good idea to have a spare filter and then just switch them over after each clean. To use a filter cleaner, simply apply filter cleaner to the filter, leave it in a bucket of hot water and then leave it for 30 minutes if it’s an instant filter cleaner or overnight if standard filter cleaner and it will be ready to use after you give it a quick hose off!


9)   Spa Flush


This product is definately a product you will want to use if you purchased a spa preowned! This is because without the spa flush, the hot tub may  still have excess water in the pipes from when it was last emptied. Using the hot tub flush will get rid of any dirt in the system and let you start afresh.

To use this simply add the recommended amount to your hot tub, turn off the air controllers and take out your filter, then turn on all your water jets and simply leave this running for around an hour, you should see a lot of dirt in the water and the spa will foam up slightly. This is normal, and all you need to do is empty the hot tub and then clean the shell out. Once this has been done, you can refill the tub with fresh water, after this process we recommend shocking the water with non chlorine shock and adding your normal sanitizer into the hot tub water. We recommend useing this product at least yearly to maintain and keep your hot tub clean!


Extra Tips!

When you add any chemicals into your hot tub,  it’s a good idea to leave the cover off and put your jets on for 5 minutes, this helps the chemicals circulate around the hot tub system and any fumes coming off wont damage the hot tub cover.