My reef actually inspired me to do that with my 36 gallon bow front.Life started in the seas. Most freshwater species are way cheaper in money and time than saltwater though. You can get that cappuccino snail i posted for under $5. Something similar in saltwater would be 10 - 20 times that. Same thing goes for fish. You could get a jewel cichlid for around $10, in saltwater you might be spending $100 or more.
Its not that you couldnt setup a freshwater tank with live rock and a refugium for various miniature invertebrates as a food supply for the fish; or that you couldnt setup a reef like structure with sponges, bivalves and various filter feeding crabs and shrimp, its just that almost no one ever does it. Which i think is a shame. A tank like that would function a lot differently than your average freshwater aquarium.
I turned the tank from some rocks and driftwood to completely planted and plan on ordering freshwater amphipods (scuds) to take care of algae and detritus better than a gravel vac ever could. I’m gonna have predators, scavengers, and dithers all mixed together.
Centerpiece will be puffers, and the amphipods are half a test to see if I will ever need to clip their teeth if I provide as close to their natural diet as possible.
So far it’s been going well, I just need to locate some of the fish I want.