My bad on that last post. That second bubble counter should pretty much just be into a check valve and into the tank. Poor quality control on my post there.
I found one major flaw in my setup while I was messing with it the other day, not one that would really solve why I'm not seeing the pressure build up, but why I was seeing such a drop in performance. A small gash had appeared in the last section of tubing going into the tank, so a lot of my CO2 was leaking there. I replaced the line and my system is functional again.
I replaced my filter with an ac20 that I don't really want to cut into right now, so I jimmy rigged a new kind of diffuser for myself. Section of capped plastic tube with floss stuffed inside and the output tube placed through the center. The co2 travels through the tube, releases into the tank and gets trapped in the floss for a longer amount of time then if it was just being put in the tank. Well see how it works.