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How to Maintain Your Water Chemistry
Keeping your hot tub or swim spa water clean, clear and comfortable isn't simply about adding chlorine or bromine. Good water chemistry comes down to testing regularly, correcting the balance in the right order, and using shock treatment when needed.
Whether you use chlorine or bromine, understanding what each chemical does — and when to add it — can make maintaining your water much easier.
So, what order should you follow?
Test → Alkalinity → pH → Sanitiser → Shock when required → Retest
Let's break it down.
1. Test Your Water First
Before adding any chemicals, always test the water.
At a minimum, check your pH, total alkalinity and sanitiser level. Depending on your spa, you may also need to check calcium hardness and other water parameters.
Testing first is important because adding chemicals without knowing your current levels can lead to over-treatment or an imbalance.
Think of your test results as your starting point. They tell you what the water actually needs.
2. Get Your Alkalinity Right
Once you've tested the water, total alkalinity is normally one of the first things to address.
Alkalinity helps stabilise your pH. If it's too low, your pH can fluctuate considerably. If it's too high, your pH can become difficult to adjust and may tend to rise.
Getting your alkalinity into the appropriate range gives you a much more stable starting point for the rest of your water chemistry.
Always follow the recommended levels for your particular pool, spa and chemical system.
3. Adjust Your pH
Once alkalinity is under control, check your pH.
For many spas, a pH of around 7.2–7.6 is commonly recommended, although you should always follow your manufacturer's guidance.
pH is important because it affects both bather comfort and sanitiser performance.
If the pH is too high, chlorine becomes less effective. If it's too low, the water can become irritating and may contribute to corrosion of equipment and surfaces.
Make adjustments gradually, allow the water to circulate, and then test again.
4. Maintain Your Chlorine or Bromine
Now it's time to look at your primary sanitiser.
If you're using chlorine, you need to maintain an appropriate free chlorine level.
If you're using bromine, maintain the bromine level recommended for your particular system.
Both sanitising systems help control bacteria and other microorganisms in the water.
But there's an important point to remember:
Your normal sanitiser level and your shock treatment are not the same thing.
Your regular chlorine or bromine maintains the water day-to-day.
Shock treatment is used periodically to deal with the additional organic load that builds up in the water.
And that's where shock treatment becomes particularly important.
5. Shock Treatment — What Is It and Why Do We Need It?
Even when your chlorine or bromine reading looks correct, your water can still contain contaminants from things such as sweat, body oils, cosmetics, sunscreen, dirt and other organic material.
This is where shock treatment comes in.
Shock treatment is a higher-dose oxidising treatment designed to break down contaminants and help restore water quality.
There are two main types you'll commonly come across:
Chlorine shock and non-chlorine shock.
And understanding the difference is important.
Chlorine Shock
Chlorine shock uses a chlorine-based product at a significantly higher dose than your normal maintenance chlorine.
Its purpose is to provide a strong dose of chlorine to deal with organic contamination and, depending on the product and application, help address microbial contamination.
Chlorine shock can be particularly useful when the water has had heavy use, become cloudy, developed an unpleasant smell, or requires a stronger sanitising treatment.
However, because you're adding a significant amount of chlorine, you need to follow the product instructions carefully and allow the required contact time before using the pool or spa.
Don't assume that because the water looks clear, it's immediately ready to use.
Always check the product label for the required waiting period and test the water before bathing.
Non-Chlorine Shock
Non-chlorine shock is different.
It is generally an oxidiser rather than a chlorine sanitiser. A common active ingredient is potassium monopersulfate, often referred to as MPS.
Its main job is to oxidise organic contaminants and help break down unwanted compounds in the water.
One of the major benefits is that it doesn't add the same type of chlorine dose as a chlorine shock.
For this reason, non-chlorine shock is often used as part of routine maintenance, particularly in spas and bromine systems.
With bromine, an oxidising shock can also help regenerate bromide into active bromine, depending on the system and product being used.
But here's something very important:
Non-chlorine shock does not replace your normal sanitiser.
If you're using a chlorine system, you still need to maintain the appropriate chlorine level. If you're using bromine, you still need to maintain the appropriate bromine level.
Think of it this way:
Sanitiser disinfects. Shock oxidises and helps deal with the stuff your sanitiser has been working against.
Some products can perform more than one function, so always check the label rather than assuming every shock product works in exactly the same way.
Chlorine Shock or Non-Chlorine Shock — Which One?
The answer depends on your water system and what you're trying to achieve.
Chlorine shock provides a strong chlorine treatment and can be useful when a more intensive chlorine treatment is required.
Non-chlorine shock is primarily an oxidising treatment and is often convenient for routine maintenance, particularly in spas and bromine systems.
Neither should simply be considered a universal replacement for the other.
The important thing is to choose a product that's designed for your particular pool or spa and compatible with your sanitising system.
6. Circulation Is Just as Important
After adding chemicals, your circulation system needs to do its job.
Good circulation helps distribute the chemicals throughout the water rather than leaving concentrated chemicals in one area.
Make sure your pump and filtration system are operating according to the manufacturer's recommendations, and keep your filter clean and maintained.
Water chemistry and filtration work together. You can have perfectly balanced chemistry, but if your circulation and filtration aren't working properly, your water may still struggle to stay clear.
7. Test Again
Finally, test the water again.
This step is often forgotten.
After making chemical adjustments — particularly after shock treatment — retesting confirms what effect the treatment has had and helps prevent you from adding unnecessary chemicals.
Don't fall into the trap of continuously adding products because "the water doesn't look right."
Test it first.
Your test results tell you what the water needs.
The Simple Order to Remember
Maintaining water chemistry doesn't need to be complicated.
Remember:
1. Test the water
2. Balance total alkalinity
3. Adjust pH
4. Maintain chlorine or bromine
5. Shock when required
6. Circulate and filter
7. Retest
And remember that shock treatment isn't just about fixing cloudy water. Used correctly, it can be an important part of a regular water-care routine.
The biggest mistake people make is thinking that more chemicals automatically mean cleaner water.
It doesn't.
Good water care is about testing, understanding what your results mean, adding the correct product in the correct amount, allowing it to circulate, and testing again.
Whether you're running a chlorine pool, a bromine spa or a swim spa, getting the order right will make your water easier to manage and help keep it clean, clear and enjoyable.
Below is a friendly chemical guide that you can download and keep for future reference.
Simply select the sanitiser you currently use in your spa to find the relevant guidance.
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