ok i only get paid once a month so i have to decide between the sump and skimmer this month. i believe that i want to set up the sump first that way when i do purchase a skimmer i can get on that goes in the sump rather than a hang on. i have a 55g FO right now. i am going to make it a reef later this year. i would like to set up about a 20g sump. will that be sufficient.