How much Shock ?

[chem geek]

No.  MPS is an oxidizer so adds oxygen to the chemical and the result of the rest of MPS is just potassium sulfate salt.  The extra oxygen on the organic makes it more polar and can either make it more soluble or have it combine with calcium or magnesium to coagulate to the filter.  For smaller molecules (depending on their specific chemistry), the MPS may oxidize it more completely to gasses such as nitrogen and carbon dioxide.

The standard Water Replacement Interval (WRI) converted into person-hours is:

WRI (days) = (1/9) x (Spa Size in Gallons) / (# of bather-hours per day)

If you use the Dichlor-then-bleach method then you can get at least double the above time in more heavily used spas because you avoid the buildup of CYA that is the main reason spa water needs to be changed more frequently with Dichlor-only.  If you have an ozonator, you may also be able to go longer because ozone will oxidize some of the bather waste so the CYA buildup from Dichlor will be slower (since less is used).

[lehacf]

Just had my water tested at "Leslie's Pool & Spa" store and was told that bromine level is at near zero. All other parameters are within norm. I have Spa Frog with bromine cartridge installed with dial set to 4. Tub has two cleaning cycles with 2.5 hours total run time. Used daily for about 30-60 minutes. Should I increase bromine level in SpaFrog cartridge or should I get a floating dispenser? Why bromine level is so low?

[chem geek]

If you are using the spa daily for 30-60 minutes (with one person?), then that would require around 7.9 to 15.8 Total Bromine to oxidize the bather waste.  If you don't have an ozonator, you'd need to add an oxidizer after your soak unless you plan to literally soak every day and want the bromine tabs to handle that load.  The problem is that they are released slowly whereas your bather waste is released much more quickly.  I presume you tested just BEFORE your soak.  If you test anytime in the hour or so after your soak, the bromine level will read very low if not zero (though usually there's some bromamine that will show up as Total Bromine).

So 30-60 minutes of one person soaking would normally need 3.5 to 7 teaspoons of non-chlorine shock (43% MPS).  Is that how much you were using?  With the tabs I would think you could add less than this amount.