Every bubble is different, BPS isn't a standard unit of measurement for CO2. If you put 4bps into a 100L tank, you're going to get very different results with 4bps in a 1000L tank. What you need to do is increase it slowly each day until the drop checker turns lime green or yellow, note how many BPS it takes to get it to this colour. This is the measurement for YOUR tank, when you need lots of CO2, you can turn it up to this level and roughly assume it will get you there. I turned mine back down when I first got fish and slowly increased it until they gasped, then turned it down so it's as high as possible without killing the fish.
Hope this helps.