sheena its all what people believe as its worked for them , basically all corals(to my knowledge) like clean water its just some are hardier to bad water conditions like zoanthids for instance.
high and low nutrient systems could either be talking about nitrates or phosphates(such as ulns) or how much organics are in the water column(perhaps feeding,ditrius etc)
some animals like elegance come from muddy laggon type waters and so people say they are " high nutrient" compared to our clean water we have in aquaria.
its all a load of crap lol
ps....told you the laid back system works , the biggest problem most of us have in reeftanks is......us lol
__________________
........
|