Drop checkers and BPS is a good way to start off, but there is no better method than watching the plants and livestock. Just remember to give it a good two or three hours between changes as the results wont be immediate. BPS can also vary from regulator to regulator, bubble counters, tubing, even bottles, so don't read too much in to what other people are running. I myself run 6 or 7 bps on a 70 litre tank, but I know others have gassed their fish at 3bps running similar equipment. Plant mass and lighting is also another factor. I have to reduce my bps after a heavy trim or the fish aren't too happy.