Congrats on the restart of the tank... somehow staghorn is growing at a rapid pace. It is known to bloom when there are high organics in the water (such as a new tank with added fish food). It seems to also favor old / damaged leaves, rotting wood … pretty much anything that leaks nutrients.I have a 75 gallon tank ... I'm about 4 days into cycling ... adding fish flakes everyday ... pressurized CO2 at about 3 BBs with EI dosing... I have no algae in my tank at all
Best thing is to remove the whole leaf, where impossible treat with Excel or H2O2 solution. In most cases after manually removing it and reducing the organic load it does not persist.
Not that this is the reason why you have algae, but 3 bubbles per second (BPS, is this what you meant ?) for a 75g is too little even with a good reactor. Do you have a drop checker ?