What type of co2? I'm guessing it's flourish excel, in which case it says on the bottle to dose either every day or every other day. If there's no plants in your tank that have special requirements I.E anubias, java fern, moss, crypts, etc I'd do every other day for the amount per gallon suggested, I think it's one capful for 50 gallons? So you could get a measuring cup and measure out 1 ml for ten gallons every other day, that is if it's flourish excel.