Built for the long haul, and backed like it
Over 10,000 AlumiTubs are out in the world, at off grid cabins, lake cottages, family homes and coastal properties across the globe. The earliest ones are still being soaked in today.
Coastal salt air. Minus forty in the north. Hard well water. Rentals running seven days a week. Cabins left alone through the winter. The design has been refined over twenty five years of tubs coming back to us with real world wear from real world places.
That track record is why we can put a 25 year structural warranty on a hot tub, and why every component is replaceable rather than disposable.
Why aluminum, and how it has always been protected
Marine grade aluminum was chosen because it holds up where other materials don't. It doesn't rely on swelling to stay watertight the way a traditional cedar tub does, and it doesn't crack or delaminate the way moulded acrylic does. Cedar stays on the outside where it belongs, doing what it's best at.
Aluminum is also a metal, and every serious marine application manages that the same way: the right alloy, sacrificial anodes where they're needed, and water kept within a defined range. Boat hulls have been built this way for a century. We've built this way since 2001, and it's why so many of those early tubs are still in service.
Now the protection is in the surface too
The aluminum in every AlumiTub is now built with a marine grade protective barrier as part of manufacturing. Earlier tubs depended on the owner following the water care and anode guidance closely. The protected surface means the tub is no longer relying on that alone.
We still publish water care ranges, and we still ship anodes, because balanced water protects the equipment, the cedar and the quality of your soak, not only the structure. The difference is that the tub is now built to handle a mistake.
Sacrificial anodes
A sacrificial anode is a block of a more reactive metal placed in the water so it corrodes preferentially. Standard practice on boats and in water heaters for as long as either has existed.
Magnesium is used because the anode has to be more reactive than aluminum to do anything at all. Anodes ship with every system that specifies them, and they're replaced every 3 to 4 months, or once around 30% remains, which falls naturally alongside a seasonal deep clean.
Water care ranges
| Parameter | Target |
|---|---|
| Calcium hardness | 150 to 250 ppm |
| pH | 7.4 to 7.8 |
| Total alkalinity | 80 to 120 ppm |
| Bromine | 2 to 3 ppm |
The one most people miss is calcium hardness. Very soft water is chemically aggressive, because it's under saturated and pulls minerals from whatever it touches. Some municipal supplies run as low as 10 ppm. If you fill through a water softener, you're below spec by design, because removing calcium is what a softener does.
Not compatible with an aluminum interior: chlorine in any form, pucks and floaters, salt chlorine generators, copper based algaecides, silver based mineral cartridges. Several of these are standard in the acrylic spa world, which is why pool stores recommend them.
Bromine at 2 to 3 ppm, hydrogen peroxide and plant derived treatments are compatible.
Earlier tubs can be brought up to the same standard
The barrier can be applied to tubs already in service. That's how we approach everything on an AlumiTub. Components are replaceable rather than disposable, and improvements go to owners who already have one, not only to new buyers. We still supply parts for tubs built two decades ago.
If you own an AlumiTub built before June 2026, or you've seen any surface change you're unsure about, email hi@alumitubs.com with photos and your water numbers. We'll tell you what you're looking at and what's involved in putting it right. We'd rather you asked than lived with it.