Really don't need any additives except a good water change weekly or at least monthly. I had my old LPS/softy tank running for 1 yr with nothing but water changes,a refugium, skimmer, and kalkreactor. I know own a 500g total volume reef tank, SPS dominated and other than a kalkreactor and calcium reactor, I do not add anything. Magnesium, and strontium from time to time, but only when I get bored and want to test something. Just maintain your parameters, ie. salinity, calcium, alk, nitrates, pH and temp and you should be fine. As for feeding, scraping the algae off the glass and normal feedings to fish will benefit the corals. If you have a good skimmer and established filtration system, you can make your own coral food. There are many recipes out there. Don't forget good lighting is also key to their survival.
Good luck