I had a JBJ 3 Gallon Picotope and kept corals in it. I stacked it top to bottom with live rock, no sand, and put live rocks pieces in a HOB filter and stuffed some Chaeto in there.
I stocked this tank with little frags of xenia, a head of frogspawn, some blue and red mushrooms, frags of zoanthids and palyothas, a tiny toadstool leather frag, and around 8 ricordeas.
I also had a half dozen hermits and some small snails. Only fish I kept in there was a wild caught Neon Dottyback. Spent a ton on this fish but it was gorgeous and wasn't shy at all.
It was great for a while since it went after some bristleworms and such. But after a quick while, I realized it was a mistake. This guy was a voracious hunter and killed every hermit crab in half a day and was flipping over my corals. Soon after, he jumped out the tank

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Besides that incident, the tank was surprisingly easy to maintain. I just marked where the waterline was and topped it off with fresh RO makeup water and changed a couple cups of water a week. No dosing...the water changes took care of everything. Temperature didn't fluctuate much since it wasn't by a window and didn't get excessive draft or sunshine. The room temperature was fairly constant.
Honestly, if I did it again, I would probably avoid fish since they add so much bioload for such a small tank. Then again, I have thought of neon gobies, maybe a bonded pistol shrimp/goby combo, citron goby, bicolor blennies, or six line wrasse.
Again, if I did it again, I'd stock it full with nice ricordea, zoanthids, and palythoas and throw in a couple of sexy shrimp and be done!
Good luck...it can be done...check out some of the reef forums...tons of people doing them. If you want, you can upgrade to a 13w bulb from JBJ.