Maybe I can help save you a little money in the long run. The biggest three problems I ever encountered with my CO2 system were:
Every connector and fitting is a potential source of a leak. Some tubing is very permeable to CO2.
After finding and fixing all the leaks in my system, I've increased the time a CO2 bottle lasts by more than 500%!
Here's some if the things I did on my "leak quest." -
I found that the bubble counter had a leak around the stem where one of the hoses hooks on. Fixed it with epoxy cement.
I found a leak in the needle valve where one of the hose barb fittings screws on. Fixed it with teflon tape on the threads.
I found that the inexpensive plastic air-line check valve I bought had a leak around a seam. I replaced it with a metal check valve designed for CO2 that had barbs with little hex nuts. You slide the nut over the tubing, place the tubing on the barb, and then slide the nut up and tighten it to make a good seal.
I found that the washers you place between the CO2 cylinder and the regulator do not last forever. They need to be replaced. I bought a bag of fiber washers from the welding shop where I get the tank refilled. 6 washers for $1.49. I now put in a new washer and leak check this connection every time I change the bottle.
Probably 1/3rd or more of my CO2 loss was NOT due to any of the things above. It was due to the silicone tubing I was using. The CO2 was passing right through the walls of the tubing. Aquarium air-line tubing is about as bad, or perhaps worse than silicone tubing. I replaced the silicone tubing with "CO2-proof" tubing from marine-monsters.com.
You can get CO2 "leak test" solution that changes colors in the presence of CO2 and apply it to the fittings/threads with something like an eye-dropper or small artist's paint brush. Look for this stuff at the welding shop or at a beverage supply company. Soapy water will do for finding "large" leaks... paint/drip it on the connection and look for bubbles.
I'm serious when I say that probably about 80% of the CO2 I was using was escaping into the atmosphere when I first set the system up.
Here's another CO2 hint:
The CO2 in the bottle is mostly liquid. (Which means it is important to leave the bottle upright.) The high pressure gauge on the regulator will read the same, so long as there is ANY liquid left in the bottle. The high pressure gauge only starts to drop when the bottle is already "empty" (i.e. all the liquid CO2 is gone).
If you have a good scale, you can get some idea as to how much CO2 you really have left by weighing a full bottle (with the regulator and everything hooked up) and then weighing it later to see how much lighter it has gotten. If you've got a 10 lb bottle, and the weight has gone down by 5 lbs, you've used up about 1/2 of your CO2.