I was gifted a 5lb CO2 tank (with no attachments) recently, and I've never used CO2 in an aquarium before. I want to start by trying the passive CO2 method with an upside-down water bottle filled with CO2 in the aquarium.
What do I need to buy for the CO2 tank so that I can just open up the tank briefly to fill up the water bottles then close off the flow immediately after they're filled? I'd like to experiment with the passive CO2 method before buying an expensive regulator first so cheaper options would be best.