Recommend Levels

Chiefblue

Active member
Oct 6, 2018
27
Bay City, MI
I was wondering if there is a specific chart for the levels in a hot tub. The one chart in pool school lists levels for vinyl, plaster and fiberglass. If you look at the levels listed in the summary at the end of “how to use chlorine in my spa” it lists a different range of levels. For instance one says adjust TA to 50 ppm and the other one says 70-90 ppm. Just wanted to know if someone has a correct level of what the numbers should be for a hot tub.
 

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
14,889
Tucson, AZ
There isn’t a specific writeup for hot tubs as it can be quite variable depending on how people run them.

For a chlorine hot tub, you would use the same FC/CYA ratio as in pool, 7.5%. For a tub with 30ppm CYA, that would yield a minimum FC of 2.5ppm. So you would want to keep your daily FC between 2.5 to 3.5ppm when not in use. How you chlorinate the tub prior to using it if after use is up to you. Some people like to soak in lower FC levels and then bump it up to a high FC level after getting out while others add chlorine prior to getting in. Either way, the FC needs to be maintained at or above the 7.5% ratio and you can only know how often to dose based on your testing and usage.

As for TA, that’s kept lower because hot tubs have A LOT of aeration and so low TA is necessary to keep the pH from rising too high. pH can vary from as low as 7.0 to as high as 8.2 and few people will notice it. So it’s not that critical to aim for a specific pH as long as you keep the TA in check.

CH is generally not an issue as most people will dump their tub water long before calcium hardness is ever an issue.
 

Chiefblue

Active member
Oct 6, 2018
27
Bay City, MI
Sounds like good advice. So I’m assuming I should follow the levels in the “how to use chlorine in my spa” summary which is CH 150 ppm. TA to 50 ppm and then just keep following the dichlor/bleach method. Does this sound about right?
 

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
14,889
Tucson, AZ
Sounds like good advice. So I’m assuming I should follow the levels in the “how to use chlorine in my spa” summary which is CH 150 ppm. TA to 50 ppm and then just keep following the dichlor/bleach method. Does this sound about right?
That is correct (y)

You can also add borates to 50ppm as well (if you want). Borates act as a high pH buffer and will slow down the pH rise in a tub. The amount of acid you need to “move” the pH lower will increase but you should then be adding acid less frequently so the total amount is the same. Borates also make the water feel “silkier” to the skin as they have a softening effect. Algae usually isn’t a problem in hot tubs but borates do have a mild algaestatic effect, so it’s a little extra insurance.
 

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