Is Their Much Difference In Treating A Hot Tub VS A Pool?

FourT4

Member
May 7, 2018
18
Illinois
I've had a 20k in ground pool for the past 3 years, and I pretty well understand how to treat it chemically, and keep the water clear. However I recently got a hot tub and it came with chemicals. The only new thing I'm unfamilar with is that it came with powder chlorine, when I'm use to using liquid shock for the pool. I guess my questions is when i run out of powder chlorine would I be okay to use the liquid chlorine that I usually buy at Menards?
 

jseyfert3

Bronze Supporter
Oct 20, 2017
679
South-Central WI
You can't use powdered chlorine (dichlor) as your sole sanitizer. Eventually it will cause the CYA to build up to an unacceptable level where you won't be able to maintain the proper FC level. You can use dichlor when you first fill a spa until you reach a CYA level of 30. At that point, you need to switch to liquid chlorine, though the CYA will drop from degradation over time with the heat and getting tracked/splashed out so you will likely need to check and add more CYA every month at least. One bottle of dichlor has lasted me many refill cycles.

I think the biggest difference between a pool and a spa is sanitizer levels (though to be fair I don't yet have a pool, this is based on what I've read on pools). Specifically, a spa burns through FC like kids eating Halloween candy. You need to get used to doing the FC test, cause you'll be doing it a lot!

Do you have a good test kit (Taylor K-2006 or TF-100) with the FAS-DPD test? You'll also want the SpeedStir, given the amount of testing you need to do.

As to care, unlike a pool, you must add chlorine after every soak! How much depends on what you keep your water temp at, how many people are in the tub, if you shower beforehand, if you wear swimsuits or not, etc. If you don't do this, chances are your FC will be zero within a few hours of your soak. Depending on the conditions, it may be zero before your soak even ends!

What I would suggest: Test FC before you get in, every time. Ensure it's in the target range on Pool Math (get the app and buy the subscription, if you don't already have it). If you're going in for a longer soak, bump it up to the high end of the target range. If you're going to have a hot tub party with multiple people for a long time, bump that FC level up to the "SLAM Target FC" level.

After the soak, test the FC, bump it back up to the high end of the target range. Note how much you added. Test FC the next morning, as some bather waste takes a while to get oxidized and causes an increased FC demand for some time after a soak. Eventually, you'll get a feel for how much to add, and you can stop testing FC immediately after you get out. You'll just get out, add the amount of chlorine you've learned to add, and test the next morning. What I shoot for is adding enough after a soak that when I test the next morning the FC is at or above the minimum target value in Pool Math.

What is your fill water TA level?
 

Jenn1215

Silver Supporter
Jul 6, 2018
30
monongahela/pa
This has been very helpful!!! Thank you!!

You can't use powdered chlorine (dichlor) as your sole sanitizer. Eventually it will cause the CYA to build up to an unacceptable level where you won't be able to maintain the proper FC level. You can use dichlor when you first fill a spa until you reach a CYA level of 30. At that point, you need to switch to liquid chlorine, though the CYA will drop from degradation over time with the heat and getting tracked/splashed out so you will likely need to check and add more CYA every month at least. One bottle of dichlor has lasted me many refill cycles.

I think the biggest difference between a pool and a spa is sanitizer levels (though to be fair I don't yet have a pool, this is based on what I've read on pools). Specifically, a spa burns through FC like kids eating Halloween candy. You need to get used to doing the FC test, cause you'll be doing it a lot!

Do you have a good test kit (Taylor K-2006 or TF-100) with the FAS-DPD test? You'll also want the SpeedStir, given the amount of testing you need to do.

As to care, unlike a pool, you must add chlorine after every soak! How much depends on what you keep your water temp at, how many people are in the tub, if you shower beforehand, if you wear swimsuits or not, etc. If you don't do this, chances are your FC will be zero within a few hours of your soak. Depending on the conditions, it may be zero before your soak even ends!

What I would suggest: Test FC before you get in, every time. Ensure it's in the target range on Pool Math (get the app and buy the subscription, if you don't already have it). If you're going in for a longer soak, bump it up to the high end of the target range. If you're going to have a hot tub party with multiple people for a long time, bump that FC level up to the "SLAM Target FC" level.

After the soak, test the FC, bump it back up to the high end of the target range. Note how much you added. Test FC the next morning, as some bather waste takes a while to get oxidized and causes an increased FC demand for some time after a soak. Eventually, you'll get a feel for how much to add, and you can stop testing FC immediately after you get out. You'll just get out, add the amount of chlorine you've learned to add, and test the next morning. What I shoot for is adding enough after a soak that when I test the next morning the FC is at or above the minimum target value in Pool Math.

What is your fill water TA level?
 
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