Sorry for necroposting... over 5 years had gone from this topic start...
For me single side sidemount is not a problem. I prefer to use steel cylinders, (10L 200bar aka HP70) - that have average negative buoyancy aroung 2 kg (4.5lbs).
So - when I need to use one tank instead of two - I just move one lead weight (1kg) from left to the right. And balance is stay the same.
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My tanks has standard regulators with octopus hoses (all of them) - around 0.8-1m length (3 ft approx). But!
Left tank has two 2nd stages, one I use, another on the tank, under rubber bands. And inflator hose.
Right tank (if I use it) has only one second stage, and nothing else. Under rubber bands on tank.
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Also I prefer to have Nx32 in the right tank, and from 6m (10ft) change gas to the right tank.
Using gas just from one tank (in the beggining), till 50 bar (725psi), allow to be comfortable as with one tank, as with two.
And I have all dive on the air, stops in the Nx32, computer I use only as air. Always (till 35m) I have enough safety for PPO2, in case of use Nx32 on the depth - I just start to ascending till 20m. It takes 1-2 min, and safe enough.
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When we planning dive till 20m (65ft) - I use just one tank. Deeper - two.
I always can share my gas with buddy. does not matter, as from the left tank, as from the right tank. or I can share my own reg.
Later, in calm, we can separate our tanks, and most simple for me - Just gave him my right tank. e.g.
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And I can use 12L "piglet" tanks (short and heavy), but it is not so comfortable, as 10L slim tanks.
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