Spa chemicals and test kits.

Aug 20, 2012

I have a new small hot tub. 130 gallons. Filled it (hard well water) and got it up to temperature. Does anyone know if the TFT test (TF-100) kits react the same to hot water as they do with cold?

My TA is around 100 and doesn't seem to want to increase to the 125 recommended in the manual.
My PH is high, 8.2, and I am concerned about trying to move it before getting TA to where it is supposed to be.
My CH is 130. They recommend 150 and I am trying to raise it.
My FC has been struggling to stay up. Only been 3 days though.

I have been told bromine is preferred for hot tubs, but I am using chlorine because a bunch of chemicals came with the hot tub and there is this silver ion thing that doesn't work with bromine.

A few questions...
Can I use the same methods to change the levels as I do with my pool? Same ideas apply? Liquid chlorine better than solid, muriatic acid, baking soda, etc.? Or should I be using spa specific chemicals? Should I be checking CYA?

Any help is welcome. First thing is to make sure I am getting accurate readings.

Thanks very much.


LifeTime Supporter
TFP Expert
Jun 7, 2011
Midland TX
Hello, and Welcome!

THe TF100 is fine for spas, but I would suggest testing when you are between heatings. If this is a stand alone spa, there are different ways to handle the chemistry. Spas are not my strength, but there are others who will answer. The way you handle the Chemistry depends somewhat on how heavily the spa is used, and how often.


LifeTime Supporter
Jul 18, 2014
Europe / The Netherlands
i'm using the TF-100 for my tub, no problem. I Always take a large smaple and by the time i get into the kitchen it has cooled down.
for maintenance i follow which has different goal values. After soak ore once a day i add 100ml liquid Chlorine 12.5%. When guest have used my tub or more people i add 150ml after soak to get passed for the next 24h
Aug 20, 2012
Thanks for your answers.

So, I am to understand that the TF-100 test kit will react to hot water the same as cold water...

I am still unsure about a few things. I have always used muriatic acid to lower my ph in the pool and liquid chlorine for a sanitizer. My hot tub manual says both of these will harm my hot tub. Is this true? If so, what do you recommend I use?

Also, do you use stabilizers in hot tubs so the chlorine does not disappear so fast?

Thanks very much.


Mod Squad
LifeTime Supporter
Platinum Supporter
TFP Expert
In The Industry
Apr 1, 2007
Sebring, Florida
A manufacturer that post chlorine and muriatic acid will harm your tub is simply foolish.

Stabilizer is used to not only extend the life of chlorine a bit but to buffer the aggressiveness of chlorine as well....your swim suits will last longer and the FC becomes somewhat easier to control.

So, I am to understand that the TF-100 test kit will react to hot water the same as cold water
How hot?:? How cold?? Certainly it will react almost the same at all normal temps and is perfectly usable for a hot tub.

chem geek

LifeTime Supporter
TFP Expert
Mar 28, 2007
San Rafael, CA USA
You do have to be careful using Muriatic Acid or any concentrated acid chemical, but that's true for pools as well. Just add it very slowly with the circulation on. If you just dump a concentrated chemical into water quickly, it can settle at the bottom and cause damage. By adding slowly with circulation, you ensure thorough mixing.

As for chlorinating liquid or bleach, the main reason the industry says not to use these in a spa is that they assume you will be using these with no CYA in the water in which case the chlorine will be to strong. By having CYA in the water first, either from adding pure CYA or from using Dichlor for a short while, you significantly moderate chlorine's strength so that it is not harsh.