A hot tub is not a small pool. It holds a few hundred gallons of water at 100–104 °F, and two or four people in it put as much sweat, oil and lotion into the water as dozens of swimmers would in a pool. That is why hot tub water needs more frequent care, but the routine itself is simple once you have it.
The levels to aim for
| Level | Hot tub range |
|---|---|
| Free chlorine | 3–5 ppm (CDC minimum: 3 ppm) |
| Bromine (if you use it) | 4–6 ppm |
| pH | 7.2–7.8 |
| Total alkalinity | 60–100 ppm |
| Calcium hardness | 150–250 ppm |
| Stabilizer (CYA) | As low as possible; the CDC recommends none |
After every soak
Bathers use up sanitizer quickly. After each use, add a small dose of chlorine (dichlor granules are the most common) or a non-chlorine shock. Leave the cover open with the jets running for 15–20 minutes so the water mixes and any gases escape. Calculate the dose with the hot tub chemical calculator.
Two or three times a week
- Test sanitizer and pH. Adjust pH first if it is out of range, then top up sanitizer.
- Keep the water level above the skimmer opening, adding water as it evaporates.
Every week
- Test total alkalinity. If pH keeps rising, alkalinity is probably too high.
- Rinse the filter with a garden hose. Never use a pressure washer, which damages the pleats.
- Wipe the waterline with a soft cloth to remove the oily ring.
Every month
- Deep-clean the filter with a filter cleaner and let it dry completely. Having a spare filter to swap in makes this easy.
- Check calcium hardness and stabilizer if you use dichlor.
- Clean the cover, top and bottom.
Drain and refill every 3–4 months
Over time, dissolved solids and stabilizer build up and chemicals stop working as well. A common rule of thumb: divide your spa's gallons by 3, then by the average number of daily users. The result is roughly how many days you can go between drains. For a 400-gallon tub used by two people a day: 400 ÷ 3 ÷ 2 ≈ 67 days.
Before draining, many owners use a "line flush" product to clean biofilm out of the pipes. After refilling, balance alkalinity first, then pH, then add sanitizer.
Chlorine or bromine?
Both work. Chlorine acts faster and is easier to measure, but dichlor adds stabilizer that builds up between drains. Bromine stays more stable in hot water and smells less, and is popular for hot tubs that are used a lot. If you switch from bromine to chlorine, drain and refill first: once bromide is in the water, adding chlorine just turns it back into bromine.
Troubleshooting
Cloudy water
Usually low sanitizer, a dirty filter or high pH. Shock, clean the filter and check pH and alkalinity.
Foam
Caused by soaps, lotions and detergent residue on swimsuits. Shock the water; if it keeps coming back, it is time to drain. Rinse off before getting in.
Strong chemical smell or itchy skin
Often a sign of too little free chlorine, not too much: the smell comes from chloramines. Shock to destroy them and keep sanitizer in range.
Skin rash after using the hot tub
Hot tub rash is a bacterial infection linked to poorly sanitized water. Stop using the tub, shock it, clean the filter and, if the problem keeps returning, drain and refill. See a doctor if the rash is severe or doesn't go away.
Safety first: Always read the product label. Add chemicals to water, never water to chemicals. Add one chemical at a time with the pump running, never mix products (especially chlorine and acid), and keep everyone out of the water until levels are back in range. Wear gloves and eye protection when handling acid or shock.
Sources and methodology
Last reviewed: November 2026. Doses are calculated from the chemistry of each product (molecular weights and available chlorine) and cross-checked against manufacturer and industry dosing charts. Recommended ranges follow CDC guidance for home pools and hot tubs.