Maybe someone accidentally bumped the one of the knobs on the tank. or, If your tank is getting near the end(check your high pressure guage) The regulator may begin to dump CO2. This usually isn't a major problem if your pressure reg is set above 40-50 psi and the needle valve is adjusted to this pressure. The problem arrises when you try to adjust the flow by lowering the pressure instead of using the needle valve to do so.
FILSTAR Pimp #2
75 gal heavily planted,50/50 Black beauty,Eco-complete substrate, Pressurised CO2 with solenoid, ph controller, AB Reactor 1000, 330 watts 9325K GE PC lighting,Ehiem Liquidoser, 2-Filstar xp3 canisters.