Do a weight check with the same type tank you will be diving with only 500psi in the tank adjust your weight so with your lungs full you float at eye level. When you exhale you should sink. You do this check any time you significantly change your equipment (tanks type/size or exposure protection) or the water salinity. (going from fresh to salt water or even different salt levels such as the Dead Sea) This is the only way to correctly find your needed weights. From that point you need to select where to stow them to set your trim so you can swim and float correctly and comfortably. Buoyancy and/or weight calculators just give you a starting point!