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.