Hi, I have 2 nano reefs of 10g and recently 1 galon with sps and lps for 10 months now. No skimmer.
The growing rate of acropora (blue hairy acro) is near a cm per month. The Galaxea has developed 20-30 new colonies all around the original polyps. Ricordeas and specially zoanthyds grow rate is huge.
As I was experimenting the 10g has DSB, and the 4g is clean of sand, both of course fishless except 2 wurdemanni in the 10g
Water changes of 1g / month, I use live food (artemia, fish, crab eggs, etc) and coraliquid to feed corals. Growing rates are good, NOx consistently indetectable. Never had cyanos, or algae explossions, and even the dsb is clean as the first day.
I believe dont using skimmer is the reason a have a huge amount of criptofauna in my systems (specially in the 10g DSB) Tons of mysids, microstars, small worms af many kinds, gammarus, etc etc. And the great thing is that of course many of them fall in the corals mouths, what is the objective of the experiment. I've fonded a huge amount of fitoplacton in the surface of the water in the microscope.
But of course exists a bad side. Well, in fact 2, one consequence of the other. Basically evaporation and hot.
Kh and CA are quite easy to maintain if you pay attention. -In fact you can easily change the whole water if necessary.
But this tiny systems run near the 86F fronteer very very easily. And of course the issue evaporation comes with salinity changes.
This is my experience at least. If you are able to pay small but consistent and continuos attention to your system, is ok.
SPS and LPS (and of course other corals, will grow) but keep in mind they are very demanding systems.
Cheers