Your pool will use some amount of sanitizer just from the natural decay of the bromine and from other environmental factors of the system itself. In other words, if you had just cleaned and filled the pool, and had a period of time before any bathers entered the water, you could test to see what the bromine demand of the pool itself would be. Say over a 24 hour period, the bromine ppm would drop from 10 ppm to 5 ppm the bromine demand would be 50%. Beyond the bromine demand of the pool itself, you will lose bromine as the bromine neutralizes bather waste, including oils, cosmetics, deodorant, soap and all the other things people put on their bodies, as well as a significant amount of perspiration, and possibly urine and feces. The idea of the three step bromine method for a private hot tub is to have the bromine tabs be dispensed at a rate that exactly compensates for the bromine demand of the hot tub, and to use oxidizer to neutralize the bather waste. Usually, oxidizer is measured and added to the water after each period of soaking. This way if the owner goes a week between uses of the tub, and then uses it several times a day for a couple of days, the bromine will stay at about the same level all the time.
This model does not fit your usage, but by following the principles involved, you should be able to work out a way to keep the bromine ppm somewhat near a desirable level. You still need to handle both the bromine demand of the pool and the bather waste. You will obviously need to be adding more bromine during weekdays while the pool is in use, and much less overnight and on weekends when the pool is empty. I have no idea what your health department requires as far as monitoring, but I would think it would be necessary to check sanitizer and pH every hour or two during the work day when the pool is in use. You really don't want to let the bromine level ever get down to zero, or even probably not below about 3 ppm or whatever level the health department requires as a minimum.
In your situation with BCDMH tabs and MPS oxidizer, a total alkalinity of 100 ppm or more, even maybe 150 ppm would help to stabilize the pH. I don't know if your chlorine/bromine feeder can dispense liquid, but if it can, using liquid chlorine as the oxidizer would make a lot of sense in your situation. Liquid chlorine, or bleach, are relatively pH neutral, so if you could eliminate the BCDMH tabs and the MPS, then you would not be fighting a dropping pH.
Hope you find some food for thought here.
Michael