By The Zagosa Team. Published .
Reviewed or updated .
Swim spas usually hold 3,000 to 6,000 litres, run at 28 to 32C in summer, and get used in short bursts of activity rather than long soaks. The shock routine that suits a 1,200-litre hot tub at 38C does not carry over as-is. Here is how to adapt it.
The dose scales with the volume
Most non-chlorine shock products quote a dose per 1,000 litres. A 4,000-litre swim spa needs four times what a 1,000-litre hot tub needs. Owners often underdose out of habit, still using the small amount that worked in their old hot tub.
Buy shock in bigger pots for a swim spa. A 5kg tub works out far cheaper than fortnightly small bottles.
Algae becomes a genuine concern
Below 30C, algae can grow if free chlorine slips. A swim spa run at 28C in summer is vulnerable in a way a hot tub at 38C is not.
Hold free chlorine at the upper end of the band (4 to 5 ppm). Add a small dose of polyquat algaecide at every refill as a preventative.
Shock weekly with chlorine, not just non-chlorine. The chlorine residual the next day is a handy algae deterrent.
Filter and cover
Swim spa filters are bigger and clog faster. Rinse weekly, soak monthly.
The cover is larger and prone to sagging over that long water surface. A central support bar (a pool noodle does the trick) under the cover stops it pooling rainwater.
When shocking, run the jets and the swim system together to circulate the whole volume. Running only the seat jets leaves the swim end uncirculated and undosed.
Common questions
Is the bromine routine different in a swim spa?
Bromine works less well at swim-spa temperatures, because the lower temperature slows its activation. Most swim spa owners use chlorine instead.
Can I run a salt chlorinator in a swim spa?
Yes, and it is a popular choice, because the lower set temperature suits the cell's longevity. Size the cell for the larger water volume.