Regarding CFCs buoyancy:
CARBONDIVE
For those non-german speakers:
10l carbondive:
300bars 900g negative freshwater, 700g negative salt water
232bars neutral freshwater, 200g positive saltwater
100bars 1.7kg positive freshwater, 1.9kg positive saltwater
The 7l is nice, small and even half full almost neutral. Gasvolume about as much as a 10l ali. If they where only available... quite now they are impossible to find (in germany).
Greets
Dirk