Ok I've got a 120 gallon FOWLR and a 55 gallon seaclear I plan on making a reef tank. I've been using a fluval canister filter and protein skimmer on both tanks. Well I don't have a protein skimmer on the 55 yet. I've been just using tap water and water conditioner but I've been looking into making or buying a sump for each tank and getting an ro/Di unit. I don't really understand them though. Does the ro/di have to be hooked up to running water constantly? Or can you just hook it up when your ready to make some water? Like say it says 100 gpd. Do you have to make that much water everyday? And how does a sump work? What all do you need to set it up? I've been trying to watch videos but they just seem to be explaining how to build them not really telling me what each section is for and everything. I would like to build one and not have to drill the tanks. So I know I'd have to get an overflow box. And what size sump is recommended for my tanks? Any help would be appreciated thanks in advance.