CO2 Leak - Regulator to Keg

[FensterBos]

I am very disappointed to be experiencing leaks on a CO2 system only 3 uses into my ownership. I've started experiencing leaking when connecting the CO2 tank to the regulator, but plumbers tape helped to create a stronger seal. I am now having a problem between the regulator and the kegs. When I have the "shut off valve" toggled to on, I can hear kind of a hissing noise that you would hear from your propane tank when you are grilling (i.e. gas being dispensed). This occurs when I am not dispensing beer and it has already claimed one of my tanks. This "hissing" stops when I toggle the shut-off valve to off, so I know it occurs somewhere between the regulator and keg. All of the hoses and nuts are screwed on tightly.
Do I need to put plumbers tape on as much as possible? Is there a chance it is the fault of coupler? Is this something any of you have had experience with?
How bad is it for me to have to use the shut off switch everytime I want beer as to not lose another full tank of CO2.
Thank you for the help!

[edramshaw]

Check for cuts in the line using a spray bottle and some soapy water. Do you have washers on all of your gas fittings?

[fnmocurtis]

Sometimes your gas seals on the coupler can leak by, allowing CO2 to escape. If it is new system,(3 uses) that's probably not it. If you are using hose clamps, it is possible to over tighten and actually cause leaks. Same can be said when tightening the nut onto the coupler of your CO2 line. Too tight can damage the rubber washer, causing a leak. Some shut off valves can leak around the stem of the valve handle.( But that's usually older, worn out ones) I like to tighten everything very lightly, then spray with the soapy water, and only tighten as needed.