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How often to change hot tub water is a difficult question to easily answer. There are just so many variables involved.

What is certain is that hot tub water will need changing out sooner or later. It’s not a job that any one looks forward to but it’s best tackled before your eyes or worse still your nose tells you it’s time to renew the hot tub water.

Owning a hot tub is just a brilliant addition to your and your families health and wellness, but along with the fun and enjoyment comes the responsibility to keep everyone safe. Of course water quality is just fundamental.

A hot tub and a pool are both closed systems, they simply filter and re-filter the water they contain. That’s pretty much where the similarity stops. The ratio of water to hot tub bather is tiny compared to a pool and the water is warm. That means hot tub water needs more attention than a pool and has to be carefully monitored for quality and hygiene.

Bacteria can flourish in the warm conditions a hot tub offers and that’s where our chemical treatment schedule comes in. We are keeping our tub sanitised to keep the unwanted bacteria guests out.

Depending on the hot tub usage our chemical treatment works well but there is a point when it will become overwhelmed and much less effective.

How Often To Change Hot Tub Water

There are several methods to trigger the decision to change out hot tub water.

Use A Little Science: 

One of the key indicators that it’s getting time to change out your hot tub water is the “total dissolved solids” (TDS) reading.

TDS is pretty much as it sounds it measures everything that is dissolved in the water. That includes chemicals, minerals and everything else that may have found its way into the system. As the system begins to overload with solids the reading will obviously increase.

Generally we are looking for a reading of 1500 PPM (parts per million) before we need to think about a water change. Much past that figure and your tub might appear a little murky or worse algae might start appearing in the corners and crevices of your tub.

TDS can be tested using the familiar test strip method we’re all used to or even better there are inexpensive digital readers for a more precise test.

HM Digital TDS-EZ Water Quality TDS Tester

HM Digital TDS-EZ Water Quality


Use A Little Math

There are a number of simple “rule of thumb approximation” formulas you can use but we like this easy one best.

(Tub Water Capacity in Gallons)  divided by  (Number of Users)  divided by  (the number three)

Of course this depends on how big the bathers are, how flaky their skin is, how oily they are etc etc. Yikes!! You know where we are coming from!!  So this is a best guess number of days.

Use The Calendar

Many owners of inflatable hot tubs have seasonal hot tub use, generally late spring to early fall.

It should be possible to to enjoy the hot tub all summer long with just one water change somewhere in mid season. Some light use tubs can last the whole season without a change. Non chlorine shock shock treatments can buy some additional time before water change .

We recommend……

Leisure Time RENU2 Renew Non-Chlorine Shock

Leisure Time RENU2 Non-Chlorine Shock


Use Your Nose !!

If it smells then it’s time change the water!! This is the easiest and lowest tech method. We definitely don’t recommend using this one though!!!

What Causes Ineffective Chemicals

Well the main cause is probably you!!! Don’t be too hard on yourself though, it’s just a fact that every time you use use the tub you leave a little bit of you behind.

Dry and dead skin, body oils and maybe residual creams, lotions, deodorants, shampoos etc etc. They’re all challenges to the hot tub filters and sanitising chemicals.

Remember our tub is a closed system, so whilst your sanitising chemicals and filters neutralise and eliminate bacteria and contaminants very effectively: over time their effectiveness reduces. Then the system becomes overwhelmed and needs a complete reset and that means a hot tub water change and a deep clean.