I am only chiming in to add another vote for what Tbone said. I went through the pony tank decision last winter. In Lake Erie the go-to is an Al30, which is worn any time a diver goes below the depth we would be comfortable doing a CESA. That is about 60 feet for most folks here. However, Tbone's posts convinced me to go with the Al40 and I am very glad I did. I rig it with standard stage rigging and a loop bungee borrowed from sidemount and it snugs up and disappears during a dive. It gives me wonderful peace of mind on a wreck at 100 feet with a current flowing and my fingers slowingly freezing. I am quite good at sticking with my buddy but there is no substitute for having one's own redundant gas down deep.
But that is for my diving. I am down deep and cold so I need more than 19 cu ft of gas if I lost back gas. That leaves 30's and 40's, and 40's are more pleasant to dive with. A warm water diver may need less, and a 19 or 13 cu ft tank is always going to be easier to travel with. For your 30 to 60 foot diving a pony is not really needed, except for the fact it is solo diving. Well, that is an entirely different set of considerations. Obviously those are best answered in an actual solo class. Otherwise I suggest analyzing your dive site risks and equipping yourself according to those risks. Are you protecting yourself against catastrophic gas loss? Entanglement? Just want to use a pony because that is something solo divers do? Also, are you diving anywhere else? Traveling suggests a smaller tank if it satisfies your gas needs, cold water deep diving would send you towards a bigger one. That is a personal decision, derived from your gas consumption and dive needs.
But that is for my diving. I am down deep and cold so I need more than 19 cu ft of gas if I lost back gas. That leaves 30's and 40's, and 40's are more pleasant to dive with. A warm water diver may need less, and a 19 or 13 cu ft tank is always going to be easier to travel with. For your 30 to 60 foot diving a pony is not really needed, except for the fact it is solo diving. Well, that is an entirely different set of considerations. Obviously those are best answered in an actual solo class. Otherwise I suggest analyzing your dive site risks and equipping yourself according to those risks. Are you protecting yourself against catastrophic gas loss? Entanglement? Just want to use a pony because that is something solo divers do? Also, are you diving anywhere else? Traveling suggests a smaller tank if it satisfies your gas needs, cold water deep diving would send you towards a bigger one. That is a personal decision, derived from your gas consumption and dive needs.
