Hi you doing!! In exactly are you thinking to build , just fish , some fish and corals or just a reef , many of the people said than aquarium under 30 gallons is hard to keep, but is not hard as it looks, i have couple 5 gallons aquariums one of them is a little fish and corals, and the other one is a seahorse tank! Making weekly water changes , checking the parameters every week or twice sometimes, i'm using ro/di water for them, a good canister filter , in one of them a water pump, and LED's light on both!! Have a good luck with your tank!!