I was very excited @ the prospect of getting a steel tank w/ h-valve, in the belief that I could shed my 19 cf pony. Further research however, indicated that the spectre of blown neck o-rings and/ or burst disks is still with me when diving one tank. I often dive alone to 135 ffw using an al80 and the pony, and was curious about how to take more air without springing for steel doubles. Should I : 1. get the single steel with h-valve ? 2. just get another aluminum 80 and double them w/ iso manifold or for that matter seperate doubles? 3.get a higher-cap steel without h-valve and continue using pony as bail-out bottle? Any help is appreciated.