Cedar Tannins and Brown Water
Brown water in a new cedar hot tub is almost always tannins, and tannins are not a problem. They are a natural compound in the wood, released into the water when warm water first meets new cedar. The water looks like weak tea. It is safe to soak in, and it clears on its own.
What matters is knowing how long it lasts, and one thing to avoid while it is happening, because that one thing is the difference between a tint that disappears and a stain that does not.
Not sure where your water is? Check your readings.
What tannins are
Tannins are naturally occurring compounds found throughout the plant world. They are what makes tea brown, what gives red wine its structure, and what colors a forest stream after heavy rain. In cedar they are part of what makes the wood so durable outdoors, because they contribute to its natural resistance to rot and insects.
Western Red Cedar is particularly rich in them. That is a feature rather than a flaw: the same chemistry that tints your first fills is part of why the wood lasts decades in wet conditions where other species would fail.
When new cedar meets hot water, some of those compounds leach out. Heat accelerates it, which is why a tub tints faster than a cold soak in the same wood would.
What it looks like, and how long it lasts
Expect anything from a faint amber tint to a color close to strong tea. It is usually most pronounced on the very first fill and fades with each one after.
Tannins typically clear after around five full water changes. Not five days, and not five top-ups. Five complete fill, use and drain cycles. Some tubs take fewer, some a little more, depending on how much cedar is in contact with the water and how hot it is run.
During that period:
- The water is safe to soak in. It is wood tannin, not contamination
- It will not stain skin or swimwear at these concentrations
- The tint will look worse in a full tub than in a sample cup, which is normal
- Do not let a fill stand longer than seven to ten days before changing it
The one thing to avoid, and why it matters
Do not add sanitizer while tannins are still present.
This is the part that matters most, and it is the opposite of most people's instinct, because brown water looks like it needs treating.
Tannins in the presence of bromine or chlorine can bond to the tub surface and leave a stain. On a tub with a metal interior in particular, that is how a harmless tint becomes a permanent mark. What would have cleared on its own in a few fills instead becomes something on the wall of the tub.
So during the tannin period, sanitizer waits. Everything else continues:
- Total alkalinity, typically 80 to 120 ppm, corrected first
- pH, generally 7.4 to 7.6 depending on your tub
- Calcium hardness, typically 150 to 250 ppm
- Sanitizer, which resumes only once the water runs clear
Keep balancing the first three throughout. It is only the last step that pauses.
If it has already stained
Being straight about this: prevention is the reliable answer, and we do not have a proven remedy to offer once a tannin stain has set on a metal interior.
What we would not do is guess. The usual instincts for a stain, an abrasive pad or an acidic cleaner, are both wrong on aluminum and will do more harm than the stain itself, because the metal protects itself with a very thin surface layer that abrasives and acids remove.
If you are looking at a stain now, send a photo and your test readings to hi@alumitubs.com. It is worth seeing rather than treating blind, and how it looks tells us more than a description will. Some marks turn out to be surface deposits that lift easily rather than staining at all.
In the meantime, keep the water balanced and keep sanitizer within range. A stain is cosmetic. It does not compromise the structure, and it does not get worse on its own once the tannin period is over.
Getting through it faster
You cannot skip the process, but you can move it along.
- Cycle the water rather than letting it sit. Each complete change removes a proportion of what has leached out. Standing water just holds it
- Run the tub warm. Heat draws tannins out faster, so using the tub normally during this period genuinely shortens it
- Filter on the fill if you have a hose filter, since starting with cleaner water means less going on afterward
- Rinse the interior between fills with a soft cloth. No abrasives, no acidic cleaners
- Be patient with the drain interval. Seven to ten days is the outside limit during this period, and shorter is better
Some owners run the first fill or two purely to cycle the wood, without soaking at all. That works, but it is not necessary, and soaking in it is part of the fun of a new tub.
Tannins later in a tub's life
Occasionally an established tub tints again, which surprises people who thought the period was over.
Usually there is a reason. New cedar has been added, a board replaced or a lid swapped, so there is fresh wood in contact with the water. Or the tub sat empty and dry for a long stretch and the surface of the wood has been refreshed by weathering. Or a leaf and needle load has been sitting in the water, because organic debris carries its own tannins and behaves the same way.
The response is the same, and so is the warning. Cycle the water, hold off on sanitizer while the tint is significant, and let it clear.
If you have an AlumiTub
Everything above applies, and the sanitizer point matters more rather than less, because the interior is marine-grade aluminum and that is the surface a tannin stain sets on.
During the first five or so fills, keep balancing alkalinity, pH and calcium hardness, and leave bromine out entirely until the water runs clear. It is a short wait for something that cannot easily be undone.
The published targets are alkalinity 80 to 120 ppm corrected first, pH 7.4 to 7.8, calcium hardness 150 to 250 ppm, and bromine 2 to 3 ppm and never above 3, which is lower than the 3 to 5 ppm typical of a conventional spa. Use bromine rather than chlorine, avoid salt chlorine generators, and avoid anything containing copper or silver.
Extra cedar boards are supplied with every tub for seasonal shrinkage. If you fit one later, expect a small and short-lived tint from that board alone, and treat it the same way. Good Clean Living Water Care is built around these ranges, and the hose filter in it is worth using from the very first fill.
Not sure where your water is? Check your readings.