I’m not really sure, but I don’t think your tank is full, and the 0/total rating is actually accurate.
I remember tanks being weird when I first started using them, and I think maybe you need to set the tanks settings to “stockpile” or something like that, to generate hydrogen constantly, otherwise the h2o2 generator is only breaking the ice when it needs more oxygen (when you lose some by opening doors), and the hydrogen is just wasted somehow.
Unless you have a hydrogen engine onboard somewhere that is on but usually not running because it doesn’t get enough fuel from your h2o2 generator
Again, sorry I can’t help more, been a while since I’ve played and never full got the hang of hydrogen anyway