Dude
Fishaholic
if you have a planted tank no fish... would it be bad do add outrageous amounts of co2 causing the plants to grow crazy
???
???
Having a tank with no fish in does mean you can have Co2 higher than normal but i dont know about outrageous amounts because of your friendly bacteria in your filter might suffocate. (dont hold me to that though lol)
Some do run high levels of CO2 when there's no fish in the tank, ie 100ppm. However if you dont have the high lighting and ferts it'll be a waste.