There are many variables that affect CO2 saturation. However (and there will undoubtedly be those who disagree with me) I'd bet my next paycheck that on a 75g tank, 2bps will be nowhere close to 30ppm CO2. If you use a drop checker, make sure to refill it with 4dKH and pH indicator solution and see how close to solid green it gets.
All I have to go by are a few tanks, the largest of which is a 30g with a Rex reactor, and, with 100% diffusion, about 3 bps (with a JBJ style counter) gives me a yellow-green drop checker color.
Looking back through the thread, I also notice that your CO2 intake is at the top of the reactor. That may be your problem. The Rex design has the CO2 intake set down a bit because it allow the gas bubbles to attempt to rise against the current, thereby being pummeled and diffused. My current reactor is about 18" high, has the CO2 intake about 1/3 of the way down from the top, is 2" in diameter, and completely diffuses CO2. I won't pretend to completely understand the physics and chemistry of it, but it clearly works.