So, I have a 17 gallon. I only use live rock and sand plus 2 Koralias, a heater, and a Kessil 350w. I don't have a sump, no protein skimmer, no filters, etc. tank had been up for almost 2 years now and everything grows pretty well in it. I have a mixed reef with SPS, softies and a couple of fish. So, if the wife doesn't want a sump, then there are other options.
Maybe it depends on fish load too. You can go sumpless like I do but you're probably not going to have a heaping crowd of fish. Maybe I'm wrong though. Maybe shaunv will correct me - i keep my sumpless systems light on swimming poop machines lol. But i also run skimmers that are some overpowered for tank size. And started with established ten year old live rock with minimal die off. That speeds up things tremendously.
I only have 1 clownfish and 1 pajama cardinal. I feel like I could add one more though. I have 2# of rock and 2 # of sand per gallon of water. And lots of GSP and anthelia taking up nutrients.
Awesome! I don't know if I can fit 40# of rock in the 20g long without it looking like a tank full of rocks but ill test it out. Iv'e got a lot of time to think about it all Oh and it will just have one fish, and many sexy shrimp. I'm hoping the zoas will export nutrients as well. Thanks for the help.