I know it's confusing! Have a read here, search for similar size tanks. Larger salt set ups usually run sumps and/refugiums. It can be confusing because there are so many different ways to do things, depending on what you what in that tank. Everyone has an opinion based on their own experience so I suggest do plenty of research, listen to peoples advise and make you decisions from there. It's good you know you are wanting a pair of clowns, it's good to have a plan to start! Live aquaria is a great website for checking out livestock too...