You’ve had the last soak of the season, the weather’s turning, and now you’re standing next to your inflatable hot tub wondering exactly how much chemical to throw in before you pull the drain plug. Too little and you’re leaving bacteria and biofilm to colonize the liner all winter. Too much and you’re just wasting product into the drain.
A 4-person inflatable hot tub typically holds between 200 and 330 gallons, depending on the model. The correct closing sanitizer dose is enough bromine to hit 10-20 ppm, or enough chlorine to hit 5-10 ppm, circulated for 20-30 minutes before you drain. This article walks through the exact math for both sanitizers, the full closing sequence, common mistakes, and what to do with the tub once it’s dry.
How Many Gallons Is a 4-Person Inflatable Hot Tub?
The dose math only works if you know your volume, and inflatable hot tubs vary more than you’d expect. A compact 4-person round inflatable often holds about 210-240 gallons, while a larger rectangular 4-person model can push 300-330 gallons. Check your owner’s manual first. If you’ve lost it, the manufacturer’s product page usually lists water capacity. Bestway’s own winterizing guide for inflatable hot tubs recommends confirming your specific model’s capacity before adding any chemicals, because even tubs marketed the same way can differ by 50+ gallons between model years.
For this article, all examples use 250 gallons as a round working figure. Scale up or down by about 10 percent per 25 gallons difference from that number.
Bromine Closing Dose for a 4-Person Inflatable
Bromine is gentler on vinyl liners than chlorine, which is one reason a lot of inflatable owners prefer it for the closing treatment even if they used chlorine all season. The target is 10-20 ppm, roughly double to quadruple your normal operating level of 3-5 ppm. That elevated level kills bacteria and breaks down organic residue before you drain, so nothing bad is colonizing the liner for the next four months.
For a 250-gallon tub, hitting 10 ppm requires roughly 1.5 ounces (about 3 tablespoons) of sodium bromide followed by a non-chlorine oxidizer to activate it, or about 1.5 to 2 ounces of bromine granules added directly. To push to 15-20 ppm for a longer storage period, bump that to 2.5 ounces of bromine granules. Dissolve granules in a bucket of warm water first, pour in with the jets running, and let it circulate for at least 20 minutes before draining.
Chlorine Closing Dose for a 4-Person Inflatable
Dichlor is the right form of granular chlorine for an inflatable hot tub – it’s pH-neutral, pre-stabilized, and dissolves fast without the harsh pH swing you’d get from trichlor. Your closing dose targets 5-10 ppm free chlorine, which is 2 to 3 times a normal weekly shock level.
For 250 gallons, 2 ounces (4 tablespoons) of dichlor granules raises free chlorine by roughly 6-8 ppm from a baseline of zero. If you’ve been running the tub recently and there’s already 1-2 ppm residual, add 1.5 ounces to top off to the 5-8 ppm range. Dissolve in a bucket of warm water, add with jets running, and circulate for 20-30 minutes. You don’t need to wait for the level to drop before draining – the whole point is that this sanitizer goes to work on surfaces and then leaves with the water.
One common mistake: using trichlor tablets as a closing treatment. Trichlor has a pH of around 2.9 and will damage the vinyl liner and inflatable seams if it sits in contact with them at high concentration. Stick to dichlor granules for any inflatable closing dose.
Bromine vs. Chlorine for Closing: A Quick Comparison
| Factor | Bromine (Granules) | Chlorine (Dichlor) |
|---|---|---|
| Target closing ppm | 10-20 ppm | 5-10 ppm |
| Dose for 250 gallons | 1.5-2.5 oz | 1.5-2 oz |
| Vinyl liner safety | Gentler | Fine at correct dose |
| Odor during draining | Mild | Moderate chlorine smell |
| Ease of use | Slightly more steps (activate if using bromide salt) | Simple: dissolve and add |
| Cost for one closing dose | $2-4 | $1-3 |
Why these differences matter: Both sanitizers do the job. If you’re new to inflatable hot tub ownership and want the simplest possible closing process, dichlor chlorine wins on ease. If you’ve been running bromine all season or you’re worried about your liner’s long-term condition, stick with bromine for the closing treatment too. Either way, the dose and circulation time matter far more than which one you choose.
Step-by-Step Closing Sequence
- Test your current water. Check pH (target 7.4-7.6) and existing sanitizer level before adding anything. Correcting pH first makes your closing dose more effective.
- Balance pH if needed. Add pH increaser or pH reducer to get into the 7.4-7.6 range. Wait 15 minutes with jets running before proceeding.
- Add your closing sanitizer dose. Dissolve bromine or dichlor granules in a bucket of warm water, then pour in slowly with the jets running. AquaDoc makes a granular dichlor shock sized for small-volume hot tubs that works well here, if you want a pre-measured option.
- Circulate for 20-30 minutes. Jets running, cover off. This ensures the sanitizer contacts every surface, including the filter housing and jet nozzles.
- Remove and clean the filter. Rinse with a filter cleaning spray, let it dry, and store it inside where temperatures won’t freeze it.
- Drain completely. Use the built-in drain valve and, once flow stops, use a wet/dry vac to pull water from low spots and the jet manifold area. Even a cup of trapped water can freeze and split the liner or fittings.
- Wipe down interior surfaces. A clean towel gets the remaining moisture off the liner. Don’t leave it damp.
- Deflate and fold per manufacturer instructions. Most manufacturers specify a particular fold pattern to avoid crease damage at the same spot every year.
- Store above freezing. A garage, basement, or climate-controlled shed keeps the vinyl from cracking in sustained cold.
For a broader look at the full process, Buds Pools’ guide to safely closing a hot tub for winter covers the drain, dry, and storage steps in solid detail and is worth reading alongside this dose-focused guide. And this complete closing guide from Net Positive Pools goes deep on water chemistry sequencing if you want the full picture from a service-company perspective.
Common Mistakes That Cause Spring Headaches
- Skipping the closing dose entirely: Organic residue and bacteria don’t just pause for winter. They keep growing slowly in the moist liner environment. Skipping the treatment almost guarantees foul, cloudy water when you refill in spring.
- Draining too fast after adding chemicals: The sanitizer needs contact time – at least 20 minutes – to actually disinfect surfaces. Drain immediately and you’ve just poured product down the drain for no benefit.
- Leaving water in the jet manifold: Inflatable tubs don’t have the same drain-back that hard-shell tubs do. A wet-dry vacuum run through the jet nozzles after draining is the only reliable way to get that water out before a freeze.
- Storing outdoors in a climate that drops below 20 degrees F: Vinyl gets brittle at sustained low temperatures and can crack at fold lines. Store inside if you’re in a cold-winter region.
- Using the closing shock as a reason to skip spring startup chemistry: Your closing dose leaves residual sanitizer on surfaces, but it doesn’t mean your spring refill is pre-treated. You’ll still need to balance and shock fresh water from scratch.
If you’ve ever refilled a tub in spring and found that it burns through sanitizer faster than it should, the problem often traces back to biofilm left over from an inadequate closing. That’s exactly the scenario discussed in the post about why your hot tub won’t hold a sanitizer reading – worth a read before you close so you understand what you’re trying to prevent.
Frequently Asked Questions
How much bromine do you need to winterize a 4-person inflatable hot tub?
Target 10-20 ppm for a closing treatment. For a 250-gallon 4-person inflatable, that’s roughly 1.5 to 2.5 ounces of bromine granules dissolved in warm water and added with jets running. Circulate for 20-30 minutes, then drain. If you’re using a bromide salt system, add enough sodium bromide to reach 10 ppm after activation with a non-chlorine oxidizer.
How much chlorine do you need to close a 4-person inflatable hot tub for winter?
Aim for 5-10 ppm free chlorine as your closing target. For 250 gallons, 2 ounces of dichlor granules raises the level by roughly 6-8 ppm from zero. Use dichlor only – not trichlor tablets, which are too acidic for inflatable vinyl liners at closing concentration.
Should you use bromine or chlorine to winterize an inflatable hot tub?
Both work. Dichlor chlorine is simpler: dissolve, add, circulate, drain. Bromine is gentler on vinyl and produces less odor during draining, making it a good choice if you’re already on a bromine system or if your liner is showing age. The circulate-then-drain process is the same either way.
Do you have to shock an inflatable hot tub before draining it for winter?
Yes, every time. Skipping the closing shock leaves organic residue and bacteria on the liner and jet surfaces. After months in storage, that contamination creates a heavy biofilm load that makes spring startup chemistry much harder and can cause persistent cloudiness or odor.
What happens if you skip the closing sanitizer dose on an inflatable hot tub?
Biofilm and bacteria colonize the liner, seams, and any internal tubing during storage. When you refill in spring you’ll typically see cloudy, foul-smelling water and sanitizer that disappears almost instantly because it’s being consumed by that biofilm. A proper closing dose costs under $4 in product and saves you from a much bigger spring chemistry problem.
Bottom Line
For a 4-person inflatable hot tub, add 1.5 to 2.5 ounces of bromine granules (targeting 10-20 ppm) or 2 ounces of dichlor (targeting 5-10 ppm), circulate for at least 20 minutes, then drain and dry completely. That one step is what separates a clean spring startup from a chemistry nightmare.