Treating water for a Redneck hot tub

Jump to latest Follow Reply
ForceFed70

ForceFed70

0
Nov 1, 2016
5
BC Canada
Hi All, Hoping you can help with getting me started on treating the water in a redneck hot tub which I'm currently building for the family cabin. The core components being a plastic 300 gallon livestock tank and a wood fired water heater/boiler made of steel and copper. I've done some researching, but cannot find information about my particular scenario.

It's a remote and rustic cabin in the woods. No services, no power for pumps, not accessible by 4x4, etc. Tub will be used for up to 5 days at a time and will be completely drained between uses. Water will be pumped from the lake to fill via a gasoline powered water pump. Lake water quality is pretty good, it's a mountain lake and a source of drinking water for nearby town, but yeah - it's untreated water.
Initially, I wasn't planning to treat the water at all. But I've since come to the conclusion that I'll need to do something.

What I've come up with so far is to do a chlorine "shock treatment" when I 1st fill the tub and allow the chlorine to evaporate off while the tub comes up to temp (expected to take 8hrs or so). Then just use one of those floating bromine dispensers to maintain. Would that be a reasonable approach to get me by for up to 5 days? In most cases it'd only need to last 3 days.
Thanks!
 
Im curious, if the tub is plastic, and the boiler is steel, how to you get the heat from the fire to the tub with no pump? Oh, you said you had a gas powered pump.... so use that?


As for treating the water, I'd use a k1000 test kit to monitor PH/chlorine. And I'd just use trichlor chlorine tabs/pucks in a floater. That would be relatively straight forward I'd think.

trichlor will cause the ph to drop, so prolly bring some baking soda with you to add to the water if the PH gets too low.

Sounds like fun!

The water will lose heat pretty fast I'd think without any insulation over the top.. Maybe you could cut out a piece of foam board to set on top when not in use.
 
Thanks so much all!

Whoa. OK, it's apparent I'm going to need to do some research. So no easy button on this eh? Even tho it's only 5 days I'll need to do water testing, etc?


Unfortunately, nothing is built yet. I'm still in the design and material gathering stage and don't have any pictures to share. But I'll make you guys a deal - I'll post a build thread if you promise to answer my myriad of newbie questions.
Until then, you'll have to content yourselves with a pic of the build site. Here's a pic of the family cabin, I plan to place the redneck hot tub to the immediate left of the deck and will modify the railing to allow access via the deck. Please excuse the mess - picture was taken shortly after spending the day working on a bedroom addition - hence the sawhorses and big piece of foamboard leaning against the deck.

asset.php
 

Attachments

  • cabin1.jpg
    cabin1.jpg
    84.3 KB · Views: 226
Wow! That place is sweet! Sure, we'll answer all the questions you've got, no prob.

So, the issue is with hot tubs is that a small amount of hot water with a few people in it can quickly breed bacteria. So, you have to get enough sanitizer in the tub to kill all the pathogens. A hot tub is a bit trickier than a pool is. 3 people in 15k gallons vs 3 people in 300 gallons is a big difference.
 
ant 83 said:
Im curious, if the tub is plastic, and the boiler is steel, how to you get the heat from the fire to the tub with no pump? Oh, you said you had a gas powered pump.... so use that?


As for treating the water, I'd use a k1000 test kit to monitor PH/chlorine. And I'd just use trichlor chlorine tabs/pucks in a floater. That would be relatively straight forward I'd think.

trichlor will cause the ph to drop, so prolly bring some baking soda with you to add to the water if the PH gets too low.

Sounds like fun!

The water will lose heat pretty fast I'd think without any insulation over the top.. Maybe you could cut out a piece of foam board to set on top when not in use.
Click to expand...

Thank-you!

I hope to use thermosiphon to circulate the water through the boiler into the tub with no pump involved. It requires careful design, but should be doable. The cabin does have a rudimentary 12V solar power system and I could install a low volume 12V pump if it comes to it.

While it's a redneck U-built tub, I hope to do a reasonably nice job of it including building skirting, insulating, and using an insulated cover of some sort. For heat loss, my biggest concern is via the boiler in the winter. It won't have a large capacity for fuel and will likely need to be filled every 4 hrs. It gets well below freezing during our Canadian winters in the mountains and I cannot allow the boiler to freeze with water still inside. Nor do I want to wake up in the middle of the night to put more wood in. That means allowing the water to continue to circulate when the fire isn't boiling (massive heat loss) or finding a way to easily drain the boiler overnight.
 
Even tho it's only 5 days I'll need to do water testing, etc?
Click to expand...

The k1000 test kit i recommended isn't very fancy. It only costs about 10 bucks, then to refill the reagents it comes out to about 2 cents to test PH or chlorine each time. The chlorine test on it isn't very accurate in my experience, and I find the PH hard to read without daylight shining through the test block.

Trichlor pucks will take some time to dissolve in a floater, so i would expect the testing and fussing about with the chlorine to just take a few minutes each day until you get an idea of what is needed.

Legionella bacteria is found in lakes and streams, and readily multiplies at temps between 68 – 122 °F. The bacteria that causes hot tub itch is also lives in soil lakes and streams as well, and will absolutely colonize any body of water at spa temps with out sanitation.

You'll want to have Chlorine in the water, and your PH in the appropriate range.


Come to think of it, chlorine is going to corrode your copper pipe, and turn your water green. I'm not sure how to deal with that.
 

Enjoying this content?

Support TFP with a donation.

Give Support
Personally, I would just carry in a bottle of Walmart bleach, it's cheap and readily available. Using bleach won't impact PH much and if the lake water is neutral, there should not be too much water maintenance other than putting bleach in after people use it since you are dumping after 5 days.

I dose my tub (370 gallons) with 12.5% liquid chlorine every day 1-2 ounces is all I use if no one is in. 2 ounces per bather once everyone is out when it sees activity.

Water volume in hot tubs is low so water quality can deteriorate fast. It would be a good idea to get a test kit that measures free chlorine. With a test kit you'll know where the lake water is to get PH in line and you'll be able to measure sanitizer levels so no one gets a rash or something worse.
 
Last edited:
Don't be surprised if your water turns bright green. Heating the water in a copper tank will do that. We filled our hot tub with water heated in metal pots over an open burner and had that problem.
 
I would not suggest using Bromine/Bromide in your setup since you are going to drain it after a few days of use. With such a short amount of use you are not going to get a Bromide bank going just using tabs/pucks in a floater. Using straight Bromide powder to establish the bank would work, but just seems like wasted money to me.

You are probably better off using chlorine via plan old bleach. It will be both cheap and easy. I would probably add a large dose of chlorine when you arrive (something close to SLAM levels) and allow it to be used up / drift downwards during initial heat up. This should clean up any cooties in the lake water. After each use add appropriate amounts of bleach to clean up bather waste. There is also a solid argument for adding a small amount of CYA to moderate the harshness of chlorine - see here Indoor pool - CYA or no CYA?

You are going to need at least a basic test kit to know what the chlorine levels are after adding bleach. Otherwise you have no idea if you killed off the lake pathogens, if you are keeping up with bather waste, or if you added way too much bleach. The first few outings I would probably test several times. At least before anyone gets it in the first time and probably again each day. Once you get the hang of how things go you can probably test a bit less.

Also keep in mind that there will likely be elevated levels of cooties in the summer vs winter. Another solid reason to have a test kit so that you can confirm the family is safely protected.
 
I think it sounds great! Get a bottle of dichlor (chlorine w/ CYA) at the pool store) - use that the first day and add enough to "shock" to about 10ppm (probably just a 2-4 teaspoons in a small tub). The next day (or that night after use) add another TEASPOON (edited) or 2 of dichlor; or 1/4 - 1/2 cup of bleach each time after use. After 5 days > drain. Pickup a test kit at the pool store and you can tell if it is 2 teaspoons or 4 etc. Only other thing to check is pH level to make sure isn't to acidic to cause damage to water heater (after you have done it a few times - should be really quick!). Not too bad all. Might need to build one at our cabin!

While you're at the pool store, you can probably buy a thermal blank to cut and put on the water for the 5 days you are there
 
Hi and love the idea of the cabin and hot tub
I have a thermosyphon hot water cylinder connected to my fire, 4.5kw boiler rated in my home and it heats up my 250l HWC in about 8 hours from cold 20 degrees to 60 degrees c. It often boils as there are only 2ppl in the house now

A couple of points to note (not sure how much you know about these systems). You need a minimum of 1:7 rise/fall with the fire at least 330mm below the bottom of your hot tub, otherwise as the fire cools it will thermosyphon in reverse

Copper pipe should be a minimum of 25mm diameter, you can do smaller but it is more difficult to do bends etc without internal diameter reduction causing issues. I have adapted the pic below to suit your situation so you can figure out the minimum diameter you would need
Thermosyphon.jpg

It is very important there is a constant rise/fall. Any flat spots in the pipework will cause hammering, air locks and possible explosions

Dont forget to allow for expansion/contraction of the copper pipe, I have tables to calculate for that and diagrams of how to design the expansion loops/bends if you want them

At least you dont have to vent your system because its an open system

Please post up your build pics, would love to see them
 
You must log in or register to reply here.
Thread Status
Hello , This thread has been inactive for over 60 days. New postings here are unlikely to be seen or responded to by other members. For better visibility, consider Starting A New Thread.
Top Bottom
Back
Jump to latest Follow Reply