My dual gauge, single stage regulator is no longer showing a tank PSI reading, and my working pressure has slowly been dropping over the past 3 days. CO2 is still being supplied to my aquarium. I was under the impression that if the tank was close to being empty (ie the gauge reading 0 psi), I would most likely experience EOTD. However, it's been running like this for a couple of days now. Do I have a leak, or is my supply of CO2 almost depleted? Mind you, this set-up has been running for a few months.