First, you need to remove all of the algae from the tank, as near as you can. Prune leaves you can't clean up, clean the substrate surface, clean the hardware and hardscape, and do a big water change. Then, realize that you can't measure the ammonia that will trigger algae to bloom - the plants will use it pretty fast, the level will be low, and it will not be uniform in the water. Are you using any form of substrate fertilizing? Have any fish died or just disappeared? Are there lots of dead decaying leaves in the tank? All of those could contribute ammonia spikes. How about fish load - is it high? Fish waste also contributes ammonia spikes.
Do you have good water circulation around the tank? You can do this with the filter output, by directing it so it makes the water circulate well, or you can add a powerhead to get more circulation. Poor circulation will cause you to have areas of the tank with low CO2.
Once you are convinced you have no sources of ammonia, good water circulation, and the algae in the tank is removed, you can work on the CO2. Raise the bubble rate by about a third, then watch the fish carefully to see if they behave differently, showing they are affected by the CO2. Also watch for new algae growths. If no new algae growths start, you are done, but if they do, and the fish are still happy, raise the bubble rate again and repeat. This may take a month of experimenting until you can see that the algae are no longer restarting after you clean out the growths. This worked pretty well for me.