CO2 bubble rate increases as cylinder is about to run out

I was wondering if anyone else has experienced the same problem. I always know when my CO2 is going to run out because a day or two before the bubblecounter starts bubbling like mad and my fish are gasping at the top of the water. Fortunately, the fix has been easy (raise outflow from the sump to give a lot of surface chop) and I have always been around.

Do all systems do this towards the end or perhaps do I need to buy another regulator?

Thanks