High TDS in Your Spa: The Overlooked Cause of Water Problems

Maintaining clear, safe spa water involves more than just keeping your sanitiser levels where they should be. Over time, various substances gradually build up in the water that can’t be removed by sanitisers or filtration alone. These dissolved materials are known as Total Dissolved Solids or TDS.

Many spa owners don’t hear about TDS until they experience water quality problems that don’t seem to improve even with the right chemical adjustments. Understanding what TDS is and how it affects your spa can help explain why even well-maintained water eventually needs replacing.

What Is TDS?

TDS refers to all the dissolved substances in your spa water.

These dissolved solids come from a variety of sources, including:

Over time, these materials continue to accumulate even if the water still looks perfectly clean.

Why TDS Matters

A moderate level of TDS is completely normal and expected in any spa. The issue arises when those levels continue to climb over an extended period of time (find our rec range) until they eventually become a problem.

As TDS increases, spa water can become more difficult to manage and your sanitiser can struggle to do its job.

You may notice:

• Cloudy or dull water
• Foaming issues
• Difficulty maintaining water balance and sanitiser levels
• Reduced bathing comfort

A simple way to think about it is like making a cup of tea. If you kept adding ingredients without ever emptying the cup, eventually the water would become saturated. Spa water works much the same way.

Why Spas Reach High TDS Levels Faster Than Pools

Spas typically develop high TDS levels much faster than swimming pools. The main reason is their relatively small water volume combined with high bather use.

A portable spa may only hold 750 to 2,000 litres of water, yet it often accommodates several people at once. Compared to a swimming pool that’s a lot of activity in a much smaller amount of water.

This means contaminants can accumulate much more quickly, placing greater demand on the spa’s smaller cartridge filters to maintain water quality.

Another major contributing factor is the higher water temperatures usually associated with Spa’s. The higher temperature draws lotions, deodorants, makeup, and skin oilsf rom our bodies and increases the amount we sweat containing urea and ammonia and dissolves all this into the water.

Because of these factors, TDS tends to be a much more important consideration in spas than residential swimming pools.

Partial Water Replacement vs Complete Water Replacement

When TDS levels become too high in your spa, the only solution is to replace the water. The amount of water that needs to be replaced will depend on the level of TDS.

Portable Spas

For most portable spas, a complete water change is usually the simplest and most effective option.

Because the water volume is relatively small, draining and refilling can often be done within a reasonable amount of time and at a manageable cost.

In many cases, changing the water every three to six months helps maintain good water quality and prevents TDS from reaching problematic levels. The recommended timing will vary depending on:

• Frequency of use
• Number of bathers
• Water temperature
• Level of spa maintenance carried out
• Spa size

A heavily used family spa may require more frequent changes than a spa used occasionally by one or two people.

A full drain and refill is also a great opportunity to use a spa pipe and surface cleaner or degreaser. These products help remove built-up residues inside the plumbing and on the surface of the shell, reducing the chance of contaminants finding their way back into your fresh water.

Swim Spas

Swim spas are significantly larger and can hold many thousands of litres of water.

Because of the larger volume, completely draining and refilling a swim spa can be less practical and considerably more expensive. Swim spa’s are often not heated to the same temperatures as a portable spa so TDS does not build up as fast. In these situations, regular partial water replacement is often a more realistic approach.

Regularly replacing a percentage of the water helps dilute dissolved solids, improve water quality and slow the ongoing accumulation of TDS.

How to Check TDS Levels

The most accurate way to check your TDS levels is to bring a water sample into our store for professional testing. We use a designated TDS meter to measure the level of dissolved solids in your spa water and assess its overall condition.

How to Slow TDS Buildup

While TDS is an unavoidable part of spa ownership, there are a few simple habits that can help slow the rate at which it builds up.

These include:

• Showering before entering the spa
• Keeping cosmetics and lotions out of the water where possible
• Maintaining correct sanitiser levels
• Regularly shocking the spa to remove some of the organic waste
• Cleaning filters regularly
• Removing debris promptly
• Avoiding unnecessary chemical additions

Small changes like these can make a noticeable difference over time and can help extend the life of your spa water.

Final Thoughts

One of the benefits of understanding TDS is that it takes some of the mystery out of spa water care. If your water becomes difficult to manage despite regular testing and maintenance, high TDS may simply be telling you that the water has reached the end of its useful life.

Knowing when it’s time for a water change can save a lot of frustration and help you avoid chasing water balance issues that chemicals alone won’t fix.

If you’re unsure about the condition of your spa water, bring a sample into the store and we’ll be happy to test it and point you in the right direction, “because everybody deserves a safe and healthy pool”.