I brought home a pair of dwarf rainbows today and put them in my 50, and I noticed there were no bubbles coming from the diffuser. Checking the tank I saw the primary pressure gauge was way low, and the solenoid was on. I'm thinking the leak must be before the solenoid, but I really don't know. I haven't been keeping a close eye on it. It's all gone, and its only been one month.
The regulator is a JBJ, attached with a perma seal washer. I guess I need to get it refilled again, and keep a close watch on it. Maybe make a leak check solution to check for leaks.