Hearing a Hissing Noise From CO2 Tank:

This is actually pretty easy to troubleshoot, as there are only a few things you need to check.

1. Start with the little o-rings that are on the keg posts. If it is dry or cracked, it will cause the problem you are describing. Very easy and cheap to replace. It's usually wise to keep a few extra o-rings on hand for this reason.
2. Check the pressure relief valve. Sometimes it doesn't get seated quite properly, and a small amount of CO2 may be escaping. Pull the valve up and reset it, making sure it is seated properly.
3. Check the poppet valves. These are visible on the tops of the keg posts, in the center of the post. If the poppet is not flush with the top of the post, it will leak. Sometimes if you just push down on it a little, the spring will reset itself and you'll be fine. Or, you may need to replace it. Again, a fairly inexpensive fix.
4. Check the o-ring around the keg lid. Again, if its dry or cracked, you need to replace it. If you've checked all of this and you are still hearing a hiss, check your hose clamps and tighten them down. These things should solve 90% of all possibilities.

Leaking Around Keg Lid:

There is a very simple way to fix this. Turn the lid around. Keg lids are more like an egg then an oval. One part is wider than the other, but it can be very difficult to tell. Make sure that you have your regulator turned up to at least to 10 PSI before doing anything. Kegs will not seal unless there is at least 10 PSI forced onto the parts (lid, poppet valves, etc.) If that is not the problem then we need to make sure the lid is on correctly. The nice thing is there is a certain way to tell every time if you have the lid on correctly.

1. Face the keg with the gas ‘in’ post to your right.
2. Insert lid into opening.
3. Pull lid handle so that it points toward you when sealed.
4. Note: If this does not work take a look at the condition of the o-ring. If it is cracked, or has dips, the lid may not seal correctly. Replace if needed.

Gauge Reading Dropped Dramatically:

If you put your CO2 tank in the refrigerator, it is unlikely that you have a leak. CO2 is a gas, and acts like a gas when stored. That means if it is kept warm, the gas expands and will give you the 700 pound reading. If you placed the tank in your refrigerator, where it is cold, then the CO2 will contract. So, it is not uncommon for a person to get a CO2 tank filled, place it in the fridge, and the pounds go down. Don’t worry, it is just the gas compressing. You will still get the same amount of CO2 as if you left it outside the fridge.

If you suspect a leak, simply fill a spray bottle with soap and water. Then, spray any connection between the CO2 tank and the keg. If you have a gas leak, the soap will start to bubble and you will know where to look. Most times you only need to tighten a fitting down to resolve the problem.