Macro algae will aborb nitrogenous compounds, so youll need algae, with light.
Or you could get a 100ml pouch of seachem purigen and throw that in there instead... will do a much better job at keeping nitrates etc.. at 0 hopefully.
Skimmer helps, means you can stock heavier and feed heavier if you so wish - removes dissolved organic solids before they turn into nitrogenous compounds.
I have a nano power skimmer on my 80L and it seems to work ok - all the rock has decaying stuff coming off it all the time, and the skimmer is skimming.
Im no expert btw, im just doing my first SW too.