I'm installing a free hot tub I got and I'm looking for ways to use it without chlorine, bromine, balancers, anti-foamers, clarifiers, etc etc. I only plan on using it on weekends and my calculations tell me it costs about $7 to heat my hot tub from cold and water is free and plentiful where I live so my thought is to simply fill it up Friday morning and drain it Sunday night. I will have a cartridge filter running at least 12 hours per day.

How quickly does hot tub water go slimy/green/smelly/cloudy?


  • Might want to also make sure you know how long it takes to heat the water. Some inflatable or portable hot tubs can have pretty slow heaters (over 12 hours to heat).
    – JPhi1618
    Commented May 6, 2019 at 20:42
  • Interesting question. Anything I read tells about how gross hot tubs can get because of the warm water and how important correct water treatment is, but I can't find anything that tells how long it takes for any of that to happen. What is your goal for not treating the water? Just to be chemical free?
    – JPhi1618
    Commented May 6, 2019 at 20:50
  • Draining the system doesn't remove all water, and the water that remains will contain both organic material and the bacteria that like eating it. You'll be culturing grossness all week, then basking in it on the weekend. Just don't.
    – isherwood
    Commented May 7, 2019 at 13:29

4 Answers 4


Fill it on Friday, and use it all weekend. On Monday you chlorinate it, and let it sit chlorinated all week. This will prevent bacterial growth from taking over your filter. Drain and refill on Friday before the weekend, and don't add chlorine. Once you're done using it for the weekend, add chlorine. Rinse and repeat next Friday before the weekend.

I assume your intentions are to not bathe in chlorine, but hopefully the use of it is acceptable to you for spa maintenance during the week when you're not using it. The small amount left over after a drain and fill is negligible, but you could even drain, partial fill, and drain again if you want to be sure. It'll definitely be less PPM of chlorine than is in city water out of the faucet, but you said that water was free, so you may be speaking about well, rain, or lake water.

If you decide to never treat the water after using it for the weekend, then remove the paper water filter from the water filter housing and replace with either nothing or a perforated metal filter instead. Without any biological control, bacterial will use a paper water filter as a petri dish and grow wild.

  • 1
    Don't know why I didn't think of this. Great idea. This way it's pretty clean on each use but I'm not bathing in the chlorine. Hopefully is stays pretty clear for the 2 or 3 days. I'll find out....
    – Noland
    Commented May 8, 2019 at 18:24
  • @Noland depending on your intended occupants, you could suggest showering immediately before using the spa. I believe that's why there are sometimes signs asking occupants to shower before using public pools.
    – Dotes
    Commented May 9, 2019 at 15:47
  • Yes, definitely building a nice outdoor shower beside it and encouraging its use.
    – Noland
    Commented May 9, 2019 at 20:12

This seems like a bad idea. The danger of hot tubs isn't that the water will get green and gross, but that warm water is a wonderful breeding ground for a wide variety of interesting microbes.

I suspect you don't need as much in the way of chemicals if you're not keeping the water around, but I don't recommend skipping the health and safety steps.


I don't think that I'd advise this route, simply because you do usually need to do a decent amount of chemical work before the tub is usable to begin with. As an example, we did a empty/replace cycle on ours before a busy Easter weekend, and even with the initial oxidiser shock, plus the typically maximum chlorine we try to add per day, it was still cloudy come the Tuesday.

From what I know now, the cycle (for us) is that the first few days of new water typically takes at least 1 oxidiser shock at the beginning, then a few days of maxing out the chlorine until it stabilises. I wouldn't want to try heavy use in that period again, and, if I did, I'd end up needing to change it out pretty much immediately afterwards.


It depends on how filthy the people going in it are. Even draining it, there will be leftover bacteria, skin flakes, insects, etc that will wait in the pipes and pump for the next fill-up.

Have you given thought to disposing of 400+ gallons of bath water every week? Depending on local code, it should probably be disposed of in a sanitary sewer or septic system.

Best of luck!

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