Thermal mass doubling as hot tub = algae party?

Envision a cold winter afternoon... You trundle out to the greenhouse. The big stock tank of thermal mass (water) is a balmy 105F. You throw off your clothes and hop in for a soak. You enjoy a verdant oasis as you watch the snow fall outside.

Now for some reality. Assuming I could control the temp or time my hot tub parties to the tank temperature, what about gunk/algae/etc growing in the water? Is there a good treatment for the water that would keep the cooties from growing in it but still be healthy for me and the plants? Initial thoughts go towards adding salt to the water but I don't know if that would work. Any ideas or experience out there?

Thanks!

Vinegar?
Apple cider vinegar?

We put a splash in dog bowls and small water troughs' to stop them going green overnight in the summer.

Thanks Andy! I did some looking on a horse forum and they suggest 1 cup of apple cider vinegar for every 50 gallons of water to keep down algae and mosquitoes. I'd assume if horses can drink that concentration it won't be a problem to hot tub in it.

(I love this forum)

Mike, you'd have the trifecta of perfect conditions for algae; heat, moisture and sunlight. Hot tubs are notorious for growing nasties, which is why they're so heavily dosed with chemicals. I don't think you'd have much luck with ACV unless you're using a LOT of it. Salt water may work, but I really don't know. I do like the idea, though.

Try talking to some hot tub retailers in your area and ask them if there are any more natural options for water conditioning. Poll a lot of them and take their advice with a grain of salt. You should also seek out any hot tub forums as they'd have much more experience and might be able to point you in the right direction.

Mike Jay wrote:Thanks Andy! I did some looking on a horse forum and they suggest 1 cup of apple cider vinegar for every 50 gallons of water to keep down algae and mosquitoes. I'd assume if horses can drink that concentration it won't be a problem to hot tub in it.

(I love this forum)

It's a whole different ballgame at hot tub temps, Mike.

Thanks Timothy, I'll check with hot tub folks around here. And I'll take what they say with a "grain of salt"

If I'm really lucky my thermal mass will get hotter than 120 during the day. I'm not sure how hot it needs to get to kill algae though. I'm also kind of hoping that some permie out there has overcome the same problem with an unsealed water thermal mass system. If I just had sealed 55 gallon drums of water, I wouldn't care if they get gunky.

Swimmers itch is caused when certain types of bacteria reach a critical level. Those that thrive at one temperature do not do so well at higher or lower temperatures.

 You are less likely to have problems if the temperature is allowed to fluctuate wildly.  Wood heated tubs are sometimes managed this way. Algae, listeria, mosquitoes and others have temperature ranges in which they thrive. The longer the water remains at the ideal temperature, the higher the population gets.

Find out the killing temperature of things that you don't want.

 The single greatest risk for untreated water held at just over 100F, is probably listeria, which causes Legionaires disease. It dies off if held for a time at 140F.  If I were heating with wood, I'd go to 160, just to be sure. No need to hold at that temperature.  Just let cool and add some cold water if necessary, when bathing in it.