I have been running skimmer less for 5 years
Display 54' x 24" x 30" Deep
Sump 44" x 19" x 20" Deep
Nutrient export is Cheato lit 24/7 with 125 watt CFL Horticultural 6500K lamp
The display has a 4" DSB and the sump has 50 Lbs of MM, no MM has been exchanged only 10 Lbs added on the top after 2 years
Ca Koralia 1501 reactor with coral 3mm sand for Elements (1501 is the 240 volt 50 Htz version)
I have gone as long as 10 months without water changes, though Ph tends to take a beating over time doing this, occasional Carbonate of soda dosing is required if Ph drops to low
Ph has been as low as 7.7, though I tend to buffer to Ph 8 6 grams ( 0.21 Ounces) lifts Ph 0.1 which I do via the RO ATU so its very slow climbing back up
I run GFO as and when required, i.e. once the glass need cleaning more frequently the Po4 will has risen past 0.03 its not required all the time and is often because I neglected to crop the Sump Algae
Nitrates always are undetectable on Salifert low range
In conclusion, you can run perfectly well with out skimmer, I feed 4 to 6 cubes of frozen food each day plus Nori for the tangs, the fish certainly are not starving
corals get some AA feed or Coral Vitaliser though rather add hock rather than a set dose, judged by eye