Unless I'm mistaken (always a possibility), you are referring to the bromine tablet dispenser built into the weir gate, which is the floating wall in front of the filter compartment. There is a little compartment on that gate in which you place bromine tablets.
What it does is contain the bromine tablets and hold them so they can sanitize the water.
You are free to use whatever you like for sanitizing. Bromine, dichlor, Baqua, etc...
You don't have to use the dispenser- I don't.