Thanks Webster1234! really helpful insight, I was wondering if it would help me be lazier with my water changes, guess I still got to do them lol. Is there a point where the refugium/sump nutrient export in theory equals nutrient input in a perfect ecosystem. Is it 1:1 in terms of gallons or would my sump have to be bigger than my display tank? No system is perfect but I'd like to create a mini fish utopia if I could �� I'm probably won't have more than 5, maybe 6 fish if I get a clown goby so I think they should be able to live in harmony without having to fight for real estate.
There is no real ratio that I know of to suggest one size is better than the other. Just make sure it is able to hold the volume of water that drains from your tank when you shut it off. Other than that, its only real purpose is to house your skimmer, and whatever other nutrient export systems you choose. The nutrient input comes from how much you feed your fish. Not the ratio of display water to sump water. The export comes from how much live rock you have in your display in addition to macro algae, rubble, corals, and whatever else consumes waste. For those that don't have a lot of live rock in the display, they can store additional live rock or media blocks in a larger sump.
When creating a fish utopia, the most important thing is choosing fish that are compatible. Choose smaller fish that stay small, like cardinals, gobies, firefish (only if you have a lid or screen), flame hawks, etc. I would avoid fish that get big like tangs, or fish that need a lot of swimming space like anthias, triggers, etc. You might even choose one or two fish that live in the lower part of the tank like a watchman goby paired with a pistol shrimp, and then something that stays toward the middle like cardinals, and finally maybe a nem with a clownfish (although they tend to get protective in too small of a space). But carefully planning your livestock will go much further toward creating your utopia than a larger sump would.