Hi Vozie. No one can tell you the bubble rate as it varies from tank to tank depending on tank size, planting density, types of plants and of course your fish. You really need a drop tester, they are cheap and easy to use. Change the indicator liquid every 4 weeks or so. Co2 should only be injected whist the lights are on and turned off preferably a couple of hours before the lights go out. The drop tester takes a few hours to give a reliable reading and I check mine late afternoon. The blue indicator will turn from blue through green to yellow as the Co2 concentration increases. Increase your bubble rate slowly, over many days, so that the colour never reaches the yellow stage, a yellowy green is what I aim for. Once you have reached yellow the indicator will not change no matter how much you overdose with Co2, I find this to be dangerous for the fish. To me, yellow is to be avoided. Finally, don't get obsessed with the plants pearling ( forming oxygen bubbles ), oxygen produced by the plants is more often absorbed into the water before bubbles are produced. Pearling does often happen after a water change as the new water can already have a high level of devolved gasses and the tank water can't absorb any more oxygen, so bubbles are visible. Sorry, I've rambled on a bit, good luck with the Co2 and your tank. Steve.
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