Doesn’t helium leak out of all containers? Ie there might not be much left if your retirement is a long way away.

reddit suggests not, unless the valve is compromised:

https://old.reddit.com/r/AskEngineers/comments/3eqnqo/will_h...

What is a “double”?

sorry, double scuba tanks, this kind of thing:

https://www.johnchatterton.com/wp-content/uploads/2013/03/cr...

I think that's the advantage of hydrogen.

I'm not sure it would meaningfully impact hydrogen prices if we had widespread hydrogen ships.

For example, you can generate fairly pure hydrogen on-demand by passing electricity through water. Hydrogen is abundant and can be generated on-demand with low-tech tools from any water source.

It won't impact helium prices. Almost no helium is used for airships today. Most goes for industrial and cooling systems.

As a fellow diver, open circuit helium mix diving is probably not going to be sustainable. We'll probably all have to switch to rebreathers soon.