Roland,
Individual buoyancy is a funny thing and depends on a lot of different factors, but -19m doesn't seem hugely surprising in salt water and w/o fins.
Fins are usually negative ballast. In fresh water, if I pack, I'm slightly positive. With WW #4 fins, packed to the max in fresh water, I sink like a rock.
You need to add nominally 3% of your body weight in ballast when you go from fresh water to salt. However, this varies w/ the salinity of the water, which I think varies with locale, season etc. A high salt level will add buoyancy.
Just to do a little comparison, in salt water with WW #4s and no wetsuit, I'm neutrally boyant at -10m. In fresh water with fins, I'm negtive at the surface. That means that I undergo a shift in neutral buoyancy level of more than 10m just by going from fresh to salt water -- and that's in the first 10 meters, where the change in buoyancy due to compression of the chest cavity is the greatest. Add in the effect of the fins and you get a few more meters so I would expect that my neutral buoyancy level in salt water w/o fins would probably be at least -15m.
Just to round the example out a little, if Jason's figure of "neutral at -10m" is for fresh water diving, then he'd probably be slightly positive at -19m in salt water.