When should you change the water in a hot tub?

If you search the internet, you’ll find countless recommendations. These range from changing the hot tub water once a month, every 3 months, twice a year, or only once a year. So what is correct? When is a hot tub water change necessary? Every recommendation is either right or wrong. Because there is no fixed time when you must or should change the hot tub water. It is completely individual, but necessary at a certain point.

There is no fixed hot tub water change schedule, but there is a necessary time

There is exactly one chemically determined time when you must change your hot tub water. That is when the water is "chemically dead." What does that mean? Your water absorbs substances. It dissolves them. Some are already in the water when filling (for example, lime, magnesium, certain metals, salt) and others you add yourself, such as hot tub chemicals as part of the hot tub water care. The hot tub water can dissolve these, but not forever.

You can imagine it like a glass of water into which we add sugar. It dissolves. The next spoonful dissolves again. But eventually, sugar crystals remain at the bottom of the glass. The water can no longer dissolve the sugar.

The hot tub water has reached its maximum dissolving capacity

And that is exactly the time when you must change the hot tub water. It can no longer dissolve chemicals either, making them almost ineffective and your hot tub water care very complicated.

How do I know when a hot tub water change is necessary?

You can measure it and you can observe when this time has come.

1. Measurement: The dissolving capacity is measured with the TDS value. TDS means Total Dissolved Solids. So total substances dissolved in the water. If this exceeds the limit (which you find in the instructions of your measuring device), the water must be changed.
2. Observation: With the total saturation of the hot tub water, a special effect occurs that can be observed. The process I call the "Champagne Effect" shows itself by the water behaving like sparkling water or champagne. When you turn on the pumps, extremely many air bubbles form (also perceived as heavy foaming), which hiss and burst at the water surface. It takes several minutes after turning off the pump for the water to clear again and for all the air bubbles floating in the water to be absorbed or released into the air. Ozone devices usually also produce many more and smaller bubbles.

Conclusion on hot tub water changes

If your measured TDS value is too high and/or your hot tub foams heavily when the pump is on, the surface hisses like sparkling water, and the water only clears after a few minutes, then the maximum dissolving capacity has been reached and you must change the water.

Can an Ego3 filter delay the water change?

Hot tub filters generally cannot influence this because they only filter suspended particles – that is, only UNdissolved substances. However, the Ego3 filter can still extend the water change interval because it also removes 0-40 micron particles from the water. If these remain invisible in the water like with cartridge filters, they slowly rot and produce acids as fermentation products of decay, which then dissolve again in the water and accelerate reaching the maximum dissolving capacity.