Congratulations. I lost about 30, and I was able to take off a little lead, from 24+ to <20 (7mm suit, back inflate BCD). I could probably do 18 now, if my one Al tank wasnt so floaty. In steel, 18 is easy, 20 is better in Al.
I think I got more overall from being in better cardio shape, which you probably are now, too. That could account for at least a few of those pounds of lead off the belt as much as the lost body weight. Your SAC rate is going to be much better, you'll be more relaxed, and you won't hold has much air in your lungs.
Like others have said, trial and error. Be patient.
I took off 2 lbs for a dive, and if I still felt heavy at the end of the dive, I planned to take off 2 more the next time, etc. I wasn't a steady progression based on lbs lost, either. I didn't take off most of the lead until much later in the weight loss. I had plateaus where I lost 10 lbs and couldn't take off any lead, and other times I was down 5 lbs and took off 2 or more lbs of lead.