Wood Hot Tub treatment - are some oxidisers milder?

[orinokai]

I have recently bought a wood-fired hot tub and I am voraciously reading posts here and elsewhere about water treatment. There's a lot of (mis)information around and I would hugely appreciate any advice.

I only intend on using the tub once or twice a month and while it always needs to be full of water so the wood remains watertight I am happy to drain and refill before each use. I don't mind bathing in fresh, untreated water; my only concern is keeping algae and mould at bay after each dip and before the next water change.

The manufacturer has advised me not to use chlorine in the tub and has instead advised that I use active oxygen and silver ions because it will be less harsh on the wood. Can this be right? Surely any oxidiser will attack the wood at sufficient concentration and so it is less about which chemical I choose and more about the amount I use?

Do I even need an oxidiser if I'm going to be draining and refilling every 2-3 weeks before each dip? Could I just use an algaecide?

 

[JoyfulNoise]

Silver ions and MPS (potassium monopersulfate) only works if the water temps are above 100F, otherwise it’s a very slow sanitizer and poor oxidizer.

Your use case — once to twice per every few weeks — really doesn’t sound like it’s worth having a tub. Letting the water sit in there stagnant means that you’ll be spending 99% of your time trying to keep it sanitary while only using it 1% of the time for any kind of enjoyment. That doesn’t sound worth it in my opinion.

Bromine might be a better choice of sanitizer in your situation but even that is going to require daily attention to keep the water clean.

Sorry, hot tubs of any kind are high maintenance. So if you’re not using it everyday, it’s really not worth it.

 

[Methuselah]

After reading Matt's reply I'm thinking there isn't a conventional solution that's worth it. So what about unconventional?

My first thought it just drain it after use, but coat inside with something waterproof but compatible with the wood (if there is any such thing).

 

[orinokai]

Yikes that doesn’t bode well, Matt. However, the fact is I have a new hot tub currently being built and shipped to me - I can’t cancel at this point so I need to find a way to look after it! I don’t mind putting in daily work if that’s what’s required, I just want to find a solution that isn’t too harsh on the wood. If I’m draining and refilling every two weeks, could I avoid shocking it and just maintain a low level of chlorine (along with balancing the TA and ph)?

Thanks Methuselah, I have looked at a vinyl liner but can only find US suppliers (I’m the UK).

 

[JoyfulNoise]

My suggestion would be to read the sticky at the top of this forum on how to use bromine in a hot tub. Bromine will likely be a bit more stable than chlorine as it’s a less aggressive oxidizer.

Wood tubs, even those made from cedar, can be difficult to maintain for the first few months until all of the tannins have leached out. It wouldn’t be surprising at all that your first few fills of water turn tea-colored and your chemistry levels will be very hard to stabilize. The tannins and other organic compounds in raw wood make it very hard to deal with. Chlorine will react with those compounds very aggressively and make it hard to keep the levels stable. Bromine may work a bit better.

You’ll need a good test kit so you’ll want to start tracking that down now.

 

[orinokai]

Thanks, that answers my initial question about whether some oxidisers are milder than others. Although I’m still confused about why, if chlorine is a harsher oxidiser, I can’t just use less of it and get the same result as bromine?

 

[JoyfulNoise]

Thanks, that answers my initial question about whether some oxidisers are milder than others. Although I’m still confused about why, if chlorine is a harsher oxidiser, I can’t just use less of it and get the same result as bromine?

Combined chlorine compounds and combined bromine compounds form at different rates and some are worse than others. Chlorine is both a fast sanitizer and a very powerful oxidizer so it will attack the wood and any organic compounds it may emit. Chlorinated organics tend to be very smelly and, in some cases, very irritating. Bromine can also form halogenated organic compounds but they may be less irritating to some people. You’ll have to experiment with it a bit.

No matter what you choose, the water needs to stay sanitizing at all times or else you risk biological contamination. Algae and molds are the least of your worries as bacteria can grow exponentially in water that isn’t properly sanitized. Pseudomonas, giardia, fecal colliforms, legionella, etc., can all grow easily and quickly in hot tub waters. Those all can be dangerous pathogens.

 

[Newdude]

+1. I'll spare you from my 'you're not only enjoying the hot tub, you're also making people soup' lecture. Use your imagination

 

[orinokai]

Thanks for your replies, folks. I read the sticky post on how to use bromine in a spa.

I think I would rather use bromine tablets for ease of use - I'm not too bothered about starting with a chlorine system for a few weeks after each water change. Similarly, because we will only be in the tub once or twice a month, it doesn't sound like I will need to shock the water weekly, because we will not be adding additional organic contaminants during this time.

So, I'd love your advice on whether this sounds like a workable plan:

1. Change the water before each use to bathe in fresh water
2. Shock the water after each use (chlorine/MPS) to destroy organic contaminants
3. Add bromine tablets every 10-14 days according to manufacturers guidelines to sanitise water

 

[JoyfulNoise]

Thanks for your replies, folks. I read the sticky post on how to use bromine in a spa.

I think I would rather use bromine tablets for ease of use - I'm not too bothered about starting with a chlorine system for a few weeks after each water change. Similarly, because we will only be in the tub once or twice a month, it doesn't sound like I will need to shock the water weekly, because we will not be adding additional organic contaminants during this time.

So, I'd love your advice on whether this sounds like a workable plan:

1. Change the water before each use to bathe in fresh water
2. Shock the water after each use (chlorine/MPS) to destroy organic contaminants
3. Add bromine tablets every 10-14 days according to manufacturers guidelines to sanitise water

Honestly all I can say is you can try that process and see how it works. I think your tub is going to get slimy during the long periods of inactive use. Bromine tablets are very acidic and if you just leave a bunch of them to dissolve over time the pH of the water is going to crash. You’ll need to make sure that the water has sufficient alkalinity in it to handle the acidity of the tablets.

Tubs are meant to be actively managed. That’s why the big acrylic ones have circulation pumps so that the water can be held at a constant temp and filtered regularly.

All you can do is give it a try and let us know how it worked out.

 

[JamesW]

If you use CYA and a low but consistent level of chlorine, the tub should stay sanitary without undue oxidation of the wood.

You can do an OCLT to see if there is anything using up the chlorine.

If you pass the OCLT, then there is probably not much to worry about.

You can get a SWG made for hot tubs to help maintain the FC levels.

You can also watch for CC levels to detect problems.

If you get CCs, a UV system might be worthwhile, but you would only want to use it enough to get rid of CCs and not when there are no CCs.

 

[orinokai]

Matt - thanks for the tip about keeping on top of the pH, will bear that in mind
James - good to know that chlorine might be okay at the right level, will investigate that too

 

[JamesW]

It says "wood-fired".

Are you heating with a wood-fired heater?

What wood would a wood fired heater use if you used a wood fired heater?

 

[orinokai]

It says "wood-fired".

Are you heating with a wood-fired heater?

What wood would a wood fired heater use if you used a wood fired heater?

Ha, yes. Heating the wood-fired tub with wood would be the plan. Whatever I can get my hands on!

 

[phonedave]

Thanks for your replies, folks. I read the sticky post on how to use bromine in a spa.

I think I would rather use bromine tablets for ease of use - I'm not too bothered about starting with a chlorine system for a few weeks after each water change. Similarly, because we will only be in the tub once or twice a month, it doesn't sound like I will need to shock the water weekly, because we will not be adding additional organic contaminants during this time.

So, I'd love your advice on whether this sounds like a workable plan:

1. Change the water before each use to bathe in fresh water
2. Shock the water after each use (chlorine/MPS) to destroy organic contaminants
3. Add bromine tablets every 10-14 days according to manufacturers guidelines to sanitise water

Here is the issue with this plan. Organics (bacteria, algae, etc.) do not just float around in the water where you can easily drain them away or destroy them. They are masters at survival, they hide in nooks and crannies, they develop organic slimes to protect themselves from sanitizers. Your wood tub is a giant sponge for them to hide in. If you drain the water, refill, and then shock, there will still likely be a host of stuff hidden in the wood.

Mechanical action is your friend. I would do the following

1. BEFORE use, bring the water up to shock level. - something such as AquaClarity or Ahhsome may be of help too - @Ahhsomeguy can tell you how it does with wood.
2. Brush the walls and floor really really well with a good stiff brush.
3. Drain and change the water
4. Shock the water again
5. Use the tub
6. Shock again
7. Add bromine tablets every 10-14 days according to manufacturers guidelines to sanitize water and maybe do something about what gets into the wood

 

[Ahhsomeguy]

Hello Orinokai: Both Joyful Noise and Phonedave's advice should be heeded. Wood tubs can harbor hard to reach bacteria that sanitizers may not be able to attack since they are embedded and protected in a slimal protective shield. Chlorine or bromine will not breach the dermal layer of the slime allowing the sanitizer to oxidize or burn away the bacteria. Would the Aqua Clarity product benefit this owner? Yes, however, it is not marketed in the UK at this time. I have a strong recommendation for this gentleman. Please contact Total Water Products in Wales. They are a huge purveyor and distributor of Ahh-Some. Speak with Paul or Wayne. They may be able to set you up with a formulation that will work like the Aqua Clarity. Since you are away for 2 weeks and back for a while and want to use the tub, your situation requires some thought as to what will be best for you.
i want to make certain that you fully understand that you may be playing with fire if you decide to leave water for periods of time with no available sanitizer. Rashes or worse can be contracted. Please exercise proper water chemistry to effectively keep your hot tub safe and healthy.

 

[orinokai]

Thanks all for your concern and replies, all of which was great advice. However, if I can draw a common thread from the responses, it’s that there is no single foolproof way to keep this thing sanitary - it will require lots of thought, lots of effort and lots of trial and error. With this in mind I’ve decided to settle up with the manufacturer, cut my losses and cancel the build. It’s becoming clear to me that I won’t have enough free time and energy to maintain the tub and I’m glad I found this out now rather than later! Thanks all, probably dodged a bullet there.

 

[Ahhsomeguy]

Smart Move on your part.

 

[Mdragger88]

After reading Matt's reply I'm thinking there isn't a conventional solution that's worth it. So what about unconventional?

My first thought it just drain it after use, but coat inside with something waterproof but compatible with the wood (if there is any such thing).

A liner…

 

[JoyfulNoise]

Sorry we couldn’t provide a better solution. But even a standard acrylic hot tub with all the pumps and controls would be hard to maintain on an occasional-use basis.