The white snot is aluminum oxide dissolved in water. The white crust is just straight up aluminum oxide. Both point to quite serious corrosion issues due to water entering the tank, which has literally begun to eat away the aluminum tank inner shell, thus creating the oxide deposits. If anyone ever sees that in their SCBAs, a recertification inspection should happen ASAP. And I doubt it would pass. Time for a new tank.
People underestimate the importance of dry air. It's not just for the health of your guns. It's also critical for the health of your tanks and lines/fittings as well. Invest in dry air, and also routinely inspect your tanks and setup for ANY evidence of moisture. Even the tiniest bit of moisture is a bad sign since it can and will build up over time.
