By The Zagosa Team. Published .
Reviewed or updated .
Inflatable hot tubs (Inflatable Spa, Cleverspa, MSpa and the like) have taken over UK gardens. The chemistry is broadly the same as a hard-shell tub, but with three key differences: small volumes of typically 600 to 900 litres, PVC liners that do not take harsh chemistry well, and weak heaters that are slow to claw back any temperature loss.
Volume changes every dose
Inflatables usually hold 600 to 900 litres, about half a typical hard-shell. That means almost every chemical dose is roughly half what you would use in a regular tub.
Reading the bottle as though it were a 1,500-litre tub is far and away the commonest cause of an overdosed inflatable spa.
Always pre-dissolve granular products in a bucket and add slowly. In a small volume, local concentration spikes much higher than in a big tub.
The PVC liner wants gentler chemistry
PVC copes less well than acrylic with low pH and high chlorine peaks. Keep pH between 7.2 and 7.6, a tighter band than the 7.2 to 7.8 used for acrylic.
Never shock above 8 ppm. PVC starts to bleach at a sustained 10 ppm.
Use bromine if you can. Its peaks are gentler and the PVC stays in better shape for longer.
Steer clear of copper-based algaecides, which can stain the liner for good.
The heater is slow to recover
The 1.5kW or 2kW heater on a typical inflatable can take an hour to win back 1C of lost temperature. That shapes how you run the tub.
Keep the cover on whenever you are not in it, and only run the bubbler while bathing, since the bubbler is a heat-loss machine.
Do not put more than two people at a time in a typical four-person inflatable. The volume is too small to absorb the load without the chemistry crashing for the next session.
FAQ
Same chemicals as a hard-shell?
Same chemistry, smaller doses. Use hot tub chemicals rather than pool ones. Brand-specific Inflatable Spa or Cleverspa products are usually the same chemistry at a higher price per kilo.
How often should I refill an inflatable?
Every four to six weeks for moderate use, much sooner than a hard-shell. The smaller volume means TDS climbs faster.