Pony Bottles

[Shooter]

Shooter, I'm assuming you were doing deco dives in the doubles setup you have in the picture though right?  So your slung tank really isn't a pony or redundant emergency air supply but rather a deco tank with a nitrox mix (50%) maybe in it?  Just curious.  Wouldn't make much sense to sling an extra tank if it just had the same gas mix as your doubles.
[/quote]

I just used this picture to show where the pony bottle would go.  Yes I do deco dives.  I usually fill my stage bottle with a 40 to 50% mix,  When I am not doing a planned deco dive. 99% when I plan a deco dive, usually with doubles My computer allows me to change gases underwater.  So even if I don't have a planned deco dive, and I go into deco, :o (I know, plan your dives and dive your plan) It's not a problem.  When dealing with large palegic fish sometimes your plans have a tendency to change :

However, just using doubles provides a good deal of redundancy 8) when I am spear fishing,  I only use one tank.  So I carry my 30 cubic ft pony for dual purpose bail-out and to assist with the decompression.I top it off using a fill whip between dives.