[Doug]

Nothing wrong with running sumpless. Geez, everyone thinks there is only one way to do a reef tank. For sure, where possible, a sump is the way to go but its not the end all of reef tanks.

I would think some live rock for the tank would be a priority. However not a must for an fish only and depending on which fish. Some form of bio filtration would then be required. A media in the canister would serve that function, the same as fresh water, although that would not be my preferred way. Using live rock & sanbed as a bio filter is better than a media closed up in a canister. It could then be used for carbon and a phoshate removed and water flow.

Be careful about gravity flow, without an overflow. Matching the return rate and downflow is almost impossible and a mess waiting to happen. If going with something like that, then perhaps drilling the tank is better.