Divers must add weight to overcome the natural buoyancy of their exposure suit and air cylinder, the air in their lungs, the type of water they’re in, and their experience level.
A nice calculator exists at Dive Buddy dot com. Just plug in the numbers, and you will be shown the amount of weight you need to overcome buoyancy. Try it out. It’s at least a starting point. You may need to experiment with adding or subtracting weight during your various dives.
The calculator allows for your weight, experience, exposure suit, scuba tank, and water type.