Notes · 6 min read
Five things that go wrong with spas, and what they mean
Most spa problems are volume problems wearing a disguise. A spa holds a fraction of a pool’s water at twenty degrees warmer, so every bather, every hour of heat and every dose of chemical has an outsized effect. Cloudy water, a failure to heat, foaming, a chlorine smell and weak jets are the five we get called about most, and four of them are usually the same underlying cause.
1. Cloudy water that will not clear
Almost always the filter, and almost always sooner than you think. A spa cartridge works far harder per gallon than a pool cartridge does, because the same volume of water passes through it many more times a day and arrives carrying far more per bather.
Rinsing a cartridge is not cleaning it. Body oils and sunscreen bind into the pleats and need a chemical soak to come out, and a cartridge that has been rinsed twenty times and never soaked is a cartridge that is no longer filtering. If the water is cloudy and the chemistry tests fine, that is the answer.
2. It will not reach temperature
Work outwards from the cheapest cause. A dirty filter restricts flow, and most spa heaters have a flow switch that shuts the element down when flow drops — so a clogged cartridge presents as a heating fault. After that: the cover. A waterlogged cover loses heat faster than the heater can add it, and covers absorb water invisibly over a few years. Lift yours; if it is heavy, that is your bill.
Only after those two is it worth looking at the heating element, the sensor or the control board.
3. Foam on the surface
Foam is the visible form of everything that has gone into the water and not come out: detergent from swimsuits washed in the machine, body lotion, hair product, drink residue. It builds up because the water volume is tiny and it has nowhere to go.
Antifoam clears it for an evening. What actually fixes it is replacing the water, and then rinsing swimsuits rather than washing them. If a spa needs antifoam regularly, it is overdue a drain.
4. A strong chlorine smell
This one is counterintuitive and worth internalising: a strong chlorine smell means there is not enough chlorine, not too much. What you are smelling is chloramine — the compound formed when chlorine reacts with the nitrogen that bathers bring in. It is the exhaust, not the fuel.
A spa that smells is a spa whose chlorine has been consumed and whose by-products are accumulating. The fix is to shock it and then to look at why demand is that high, which usually comes back to how long it has been since the water was changed.
5. Jets that have lost pressure
In order of likelihood: air lock in the plumbing after a refill, a filter that needs cleaning, a water level too low for the skimmer to stay submerged, closed or partially closed valves, and only then a failing pump. The first four are free to check and the fifth is not, so check them in that order.
The thing underneath four of these
Water age. A spa's water is doing something a pool's water never has to: absorbing a very heavy bather load into a very small volume at high temperature. There is a useful rule of thumb — take the gallons, divide by three, divide by the number of people using it daily, and that is roughly how many days the water has. For most household tubs it lands between two and four months.
Water that has stopped responding to chemicals is not a chemistry problem to solve. It is water telling you it is finished.
Attached spas have a sixth problem
A spa that shares a pool's equipment adds valves and actuators to the list, and those fail in ways that are easy to misread — a spa that drains back into the pool overnight, or one that will not switch over, is usually a valve rather than anything to do with the water. Just over half the pool properties across our service area have a spa, so this is common.
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