electrolysis co2 systems

[ouchia]

i just bought a smaller carbo plus unit for my 20g... on the side there is a gradation of 0-300... anyone know what i should set this at? i have a fair amount of plants, and my ph is currently way too high... trying to slowly get it down with distilled water, but should i crank up my co2 also? i just put some riccia in the tank, so i want to keep this alive... i'll attach a photo...