Entry level regulators and needle valves are known to not be as high precision as systems that are more expensive (i.e. GLA regulators), so I try to limit my expectations. IME owning 3 aquatek mini regulators, the bubble count can fluctuate from what you last set it to, especially after initial setup on a new regulator. The mini regulators don't have adjustable working pressure as their full-sized siblings, but from what I've seen from those who own them, coupled with my experience, they eventually start staying on the BPS rate you set them on after an unexplained 'break in' period. Just today I had to readjust a needle valve on 1 of 3 of them back to 2 BPS. I had it on 2 BPS about two days ago... today it was less than 1 bps on a 80% full paintball CO2
It doesn't bother me all that much. I've come to expect this less than perfect performance due to the value in which I've paid for them. I just make it part of my routines to fertilize, check CO2
levels (bps and such), and feed the fish... everyday.