GMSgrowsanswered grow question 4 years ago You can put 5 gallons through and that still wouldnt be overwatering. Overwatering is keeping your medium wet all the time, not putting water through it when it needs it. Keeping it constantly wet starts oxygen deprivation and your roots start to smother and then rot. So no worries how much you put through when they need it, just let them dry some inbetween. Hope I explained this good enough for you. Cheers