Is this a far -fetched idea? We're noticing after we use the spa once, the bromine reading goes to 0. With a bromine tab floater I'd think that shouldn't happen. The spa isn't quite level and after use, we often have to add several inches of water. After a few times of that, could it be possible the bromine bank is depleted? (This is at a vacation rental that can have 6 guests there at a time , often staying 2-4 nights. It's not checked when they are there, just when they leave and I always check daily when i am staying there .)