· by Michael Blair, Nashville's Pool & Spa
A hot tub holds a few hundred gallons of water at body temperature, and every use adds sweat, lotion, detergent from swimsuits and skin cells to it. In winter it gets used more and the cover stays on longer, so the water is worked harder and ventilated less. Keeping it clear is a matter of routine, and keeping the plumbing from freezing in a Middle Tennessee cold snap is a matter of knowing what the tub does when the power goes off.
Why hot tub water goes bad faster than pool water
A pool has tens of thousands of gallons and a hot tub has a few hundred, so each bather represents a far larger load. Warm water accelerates every reaction, sanitizer is consumed faster, and the aeration from the jets drives off chlorine and raises pH. The cover traps everything that off-gasses. A tub used by four people for an hour has taken a bigger hit than a pool used by a party.
That is why hot tub chemistry is checked several times a week rather than weekly, and why the water is replaced on a schedule rather than being kept indefinitely. Total dissolved solids build until the water simply cannot hold sanitizer effectively, and no amount of chemical fixes that.
The routine
Test sanitizer, pH and alkalinity two or three times a week and after every heavy use. Add sanitizer after use rather than before, so it is working while the bather load is fresh. Shock the water weekly to oxidize what the sanitizer has combined with. Rinse the filter every couple of weeks and chemically clean it monthly, because a filter loaded with body oils is the most common reason a tub goes cloudy despite good chemistry.
Drain and refill every three to four months with normal use, sooner with heavy use, and flush the plumbing with a line cleaner before draining, because the biofilm in the pipes is what reseeds the fresh water. Nashville tap water is on the hard side, so on refill test hardness and adjust, or the heater scales.
- Test two or three times a week, and after heavy use
- Sanitize after use, shock weekly
- Rinse the filter fortnightly, deep clean monthly
- Drain, flush the lines and refill every three to four months
Cloudy water, and what it usually is
In rough order of likelihood: a dirty or worn filter, low sanitizer after heavy use, high pH or alkalinity out of range so the sanitizer is not working, old water with high dissolved solids, or a biofilm in the plumbing. Check in that order. Foam on the surface is detergent and body products, and a defoamer masks it while a water change fixes it.
Cloudiness that clears with a filter clean and a shock was a filter problem. Cloudiness that returns within a day or two on water more than three months old is telling you it is time to drain. Chasing it with clarifier at that point costs more than the water.
Freeze protection
A running hot tub does not freeze; the heater and circulation keep it warm and most tubs have a freeze protection mode that runs the pump when the temperature falls. The risk is a power cut or an equipment failure in a cold snap. Our winters bring a few nights well below freezing each year, and a tub with a dead heater and still water can freeze the plumbing and crack the pump housing within a day or two of that.
If the power is off for more than a few hours in freezing weather, keep the cover on and closed, and if the outage looks long, a small heater in the equipment bay run from a generator, or a full drain and blow-out of the lines, are the choices. A tub that is being left unused through the winter should be drained, the lines blown out with a shop vacuum or a compressor, antifreeze rated for spas added to the lines, and the cover secured. A half-drained tub is the worst of both.