The Aluminum Hot Tub Care Sheet
If you look after an AlumiTub for someone else, this page is for you. It takes about two minutes and covers everything that matters.
Most of what applies to a conventional hot tub applies here too. There is one difference, and everything else follows from it.
1. What this tub is
The inside of this tub is marine-grade aluminum, not acrylic or fiberglass. The cedar you can see is the outside.
That matters for one reason: aluminum is a metal, and a few products that are completely standard in an acrylic spa will damage it. Not gradually, and not in a way that shows up straight away, which is why it is worth knowing before rather than after.
The upside is that it is simpler to look after than most tubs. There are no jets, no internal pipework and no filter chamber, so there is nowhere for anything to build up out of reach. Draining and rinsing genuinely resets it, and the water needs less treatment than an acrylic spa does.
2. It runs on bromine
Bromine, 2 to 3 ppm. Never above 3.
That is lower than a conventional spa, which usually runs 3 to 5 ppm. The lower ceiling protects the aluminum as well as the skin of whoever gets in.
Bromine tablets go in a floating dispenser. Keep the dispenser moving freely rather than resting against the side or a bench, and take it out before anyone soaks.
3. The four numbers
Test two to three times a week if the tub is in regular use, and before anyone gets in if it is used occasionally. Correct them in this order, because each one affects the ones after it.
| Order | What | Range | What it does |
|---|---|---|---|
| 1 | Total alkalinity | 80 to 120 ppm | Holds pH steady. If pH keeps drifting, this is why |
| 2 | pH | 7.4 to 7.8 | Decides whether the water is comfortable and whether the bromine works |
| 3 | Calcium hardness | 150 to 250 ppm | Too low and the water pulls minerals out of the tub itself |
| 4 | Bromine | 2 to 3 ppm | Keeps the water safe. Only works properly once the first three are right |
Correcting bromine before the other three is the most common mistake and mostly wastes product. Add one thing at a time, dissolve it in a bucket of tub water first, circulate or stir for fifteen to twenty minutes, then retest before adding anything else.
Two notes on the fill water. If it comes from a rainwater tank or through a water softener, it will arrive with almost no calcium hardness and needs correcting on every fill rather than occasionally, because water that soft is aggressive toward aluminum. A softener strips calcium by design, so use an unsoftened tap if there is one.
4. The never list
These are the ones that cause damage. Everything else on a pool store shelf is a judgement call; these are not.
- No chlorine, in any form. Not liquid, not granular, not tablets, not pucks, not floaters
- No salt chlorine generators. They make chlorine continuously and raise chloride at the same time
- No copper or silver products. That includes copper-based algaecides and silver mineral cartridges
- No vinegar, and no descalers or acidic cleaners. Vinegar appears in a lot of general hot tub advice and it attacks the aluminum surface rather than cleaning it
- Nothing abrasive. No scouring pads, no wire wool, no pressure washing. The metal protects itself with a very thin surface layer and abrasives take it off
- No bath salts or Epsom salts. They belong in a bathtub
- Never two tablet types in one dispenser. Mixing bromine and chlorine tablets is dangerous, not just ineffective
To clean it: a soft cloth and a mild plant-based cleanser on the aluminum, wiped while still wet and rinsed off thoroughly. A soft-bristle brush on the cedar. That is the whole job.
5. If it has a firebox
Only applies to Wood Fired and Hybrid tubs. If there is no firebox inside the tub, skip this.
Never light the fire before the tub is full. Fill to the line marked on the tub, or at least 4 inches (10 cm) above the chimney collar, and keep the water there the entire time the firebox is hot. Firing it below that line damages the firebox and takes the tub out of service.
Never drain below that line until the firebox has completely cooled.
Otherwise: burn only clean, dry, untreated wood. No treated or painted timber, nothing with nails in it, no pellets or fire starter logs, and no driftwood. Clear the ash out regularly with the scoop that came with the tub, since a firebox full of ash draws badly and heats slowly.
6. Where to look things up, and where to ask
There are QR codes on the tub itself. They link to the care instructions, so anything you need is a phone camera away while you are standing in front of it.
Beyond that:
- To check where the water is, the water diagnostic takes your readings and tells you what to correct and in what order
- For the detail behind any of it, the Water Care Academy explains each number and what goes wrong when it drifts
- For the products, Good Clean Living Water Care is built around these ranges and around aluminum, so nothing in it needs checking against a label. Bromine is the exception and is bought separately
- For anything else, email hi@alumitubs.com. Questions from caretakers, property managers and contractors are welcome, and answered
If you maintain pools and spas professionally
The short version: treat it as a bromine tub with a metal interior. Alkalinity 80 to 120 ppm, pH 7.4 to 7.8 and the lower half of that range is the safer place to sit, calcium hardness 150 to 250 ppm, bromine 2 to 3 ppm.
Aluminum is amphoteric, so its protective oxide layer is least stable at both extremes of the pH scale. Soft water is the risk people underestimate: below roughly 100 ppm calcium the water is under-saturated and will draw minerals out of the metal.
No chlorine, no salt cells, no copper or silver, no acidic cleaners. Everything else is conventional.
If you have not worked on one of these before and want to check something before you treat it, we would rather hear from you than not. hi@alumitubs.com.