"Ideal" Chemisty for Hot Tub

steve_h

Active member
Aug 9, 2007
41
Chesapeake, VA
I just refilled the hot tub and am in the process of balancing the water chemistry.

I am using a 3 step Bromine method, muratic acid and Simple Blue Power Cal from the pool store for my chemicals. The hot tub is a Jacuzzi 365.

I see many posts on the pool side on correct pool chemical levels.
I really did not see a post detailing "ideal" hot tub chemistry.

Is there an "ideal" chemistry for hot tubs?
 

benavidescj

LifeTime Supporter
Apr 27, 2010
431
Fleming Island, FL
It is the same as that for a pool except that you use bromine instead of chlorine for sanitizer. CYA is only applicable to chlorine so you can ignore it. So if the hot tub (Jacuzzi) is fiberglass you would use the fiberglass pool levels:

FC 3-7
pH 7.5-7.8
TA 70-90+
CH 220-320
CYA 30-50 (ignore)

You use the same tube in the test kit to measure the bromine level. On the test vial you will normally see chorine on the left and bromine on the right. The bromine level is 2.25 of FC. So if your Bromine level is reading 5 then your FC equivalent is 5/2.25 or 2.2.
 

chem geek

TFP Expert
LifeTime Supporter
Mar 28, 2007
12,082
San Rafael, CA USA
The TA might need to be adjusted lower given aeration in the spa, but you can just see how it goes. If the pH tends to rise over time, you can have the TA lower (which it will do over time when you add acid to lower the pH). Just don't let it go below 50 ppm. If the pH tends to fall, you can set the TA higher.

The CH should be around 120-150 ppm to prevent foaming and should NOT be as high as with pools since the higher spa temperature will create a greater tendency towards scaling. If you have your TA be very low, then you can have a higher CH if you want. You can still calculate the saturation index using The Pool Calculator to make sure it's not too high.
 

steve_h

Active member
Aug 9, 2007
41
Chesapeake, VA
Thanks for the replies.

My pH does seem to rise, so I will keep it at the low end of the TA.
The house water is alkaline. I should probably test just the raw water from the well. But I am sure it in the 400+ TA and higher pH, like 8.2 and very soft and of course, zip.doodoo of any sanitizer.
Thank gawd for the RO system.

I use the pool calculator and love it.

We'll see how the battle goes.
 

PaulR

LifeTime Supporter
Jan 11, 2009
1,966
Cupertino, CA
I put 50ppm borates in my tub, it makes the pH vastly more stable. It has been 2+ months since my last water change and in that time pH has crept up from 7.5 to 7.7. TA runs in the 50-60 range.
--paulr
 

gosusgo

Member
Jun 12, 2010
23
Hi everyone! I am new to BBB this year and used it to make my pool (and my life) a lot easier this summer. Now I am re-opening a 200 gallon fiberglass hot tub using chlorine. I am getting there but need a bit of feedback. My most recent readings are as follows:
FC 10 - just added bleach bc the reading was low
CC 2
CH 70 - have been adding calcium chloride to bring it up from 0
ph 7.8
TA 140 - was also very low and slowly added baking soda which caused this and ph to rise

I am guessing I need some di-chlor to raise my CYA (not measured yet) an keep FC stabilized. Is this correct? Also, are my ph and TA levels ok to go in the tub?
 

chem geek

TFP Expert
LifeTime Supporter
Mar 28, 2007
12,082
San Rafael, CA USA
Unfortunately, you should not have raised your TA level quite so high. It's only going to cause the pH to rise. Yes, you should use Dichlor as your chlorine sanitizer for perhaps a week or so to accumulate 30 ppm CYA (about 33 ppm FC cumulatively added over the week). This will reduce the active chlorine concentration so that the chlorine isn't too strong -- it will reduce the rate of oxidation of swimsuits and skin and the hot tub cover. Since the net use of Dichlor is acidic, the TA will drop by around 12 ppm and the pH may get lower which is fine in the short-run. However, when you then switch to using bleach, you may find the pH rises too fast and will need to lower the TA via the Lower Total Alkalinity procedure which fortunately is very easy in a hot tub since you can aerate the water using jets.

The CH might be OK where it is now if you don't find that the water tends to foam. If you do see too much foaming, then you can raise the CH to 120 - 150 ppm. You don't want it higher as you want to prevent scaling in case the pH rises too much.

You should read Using Chlorine In A Spa for more info. The high CC may indicate that you did not decontaminate your spa if you just started using it. You need to decontaminate first because there can be a buildup of biofilm that will cause high chlorine demand and not be sanitary. Note also that the Dichlor-then-bleach method works best when you have a lower TA (as low as 50 ppm, if necessary) and use 50 ppm Borates (from Boric Acid such as in ProTeam Gentle Spa) for additional pH stability.
 
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