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I hope that you all realise that every time you manhandle manifolded tanks to a pool or for a two dive primer
that means that inversely you are sacrificing your ability over your lifetime to conduct those dives in the wilds
as you will have unnecessarily worn yourself out not diving
Yes, but not in the way you're thinking. Two tanks is not only extra mass on your back, but also another first stage regulator, a larger wider wing, and a couple more valves to manage. There's no special card or handshake to get doubles filled, but you owe it to yourself and your dive buddies to arrive at a level of comfort with that configuration before you just go off diving a doubles configuration. There's also no Scuba Warden asking you for your doubles card before pulling back the velvet rope at your local dive spot.Isn't doubles a specialty equipment that requires special training?
But conversely, if you spend all of your time doing, it will likely impact your ability to actually make progress.