As my tank gets older I try more and more to keep it as natural as I can. I collect my water right at the surf and do little to it except strain out the floating debris and fine mud so I can have a clear tank.
(I did use ASW for about 40 years)
I try to feed only foods from the sea like clams but I do use white worms occasionally because I can't collect enough salt water worms.
I take mud and seaweed from a bay and throw it in for bacteria. Never from a bottle.
When I started my tank I took rocks from the sea as live rock was not available then.
I use a reverse undergravel filter because I want oxygen all over the tank and under the gravel.
I never quarantine and feel parasites, bacteria, viruses etc. are natural and needed for tank health.
I try to collect live amphipods, worms etc. when I can for the gut bacteria which I feel almost totally controls fish immunity.
I add rust from iron nails for iron. (I know, not very scientific but the sea is loaded with iron and it gets eliminated in a tank if you have an algae scrubber as I do)
I use some ozone in my skimmer which I feel is natural as the sea is constantly bombarded by lightning.
I never use additives or medications of any type but I do add some calcium, alk and Epsom Salts for magnesium.