you will need a skimmer and with a skimmer the insump skimmers are better. Sorry to see you don't want to do a sump makes dosing Alk
, calcium, mag etc a lot easier. Some things you don't want to just pour into a tank that can damage coral. Plus it takes the heater, skimmer etc out of DT and gives more room and looks better and y0u can add an ATO system which helps a great deal in stability of the tank. Which is very important with corals.You will need better lighting for sure. Only additives you should need are ALk
, Calcium, and Mag. How are you on power heads or general flow of the tank.