Additives to the reef tank?

[edikpok]

I just wanted to get your opinoin with regards to trace elements and iodine additives.

I have a 12g nano cube with: goby, cardinalfish, cleaner shrimp, some hermits, pom pom crabs, candy canes, anthelia, zoos, xenia, mushrooms, gsp and some other soft corals. I don't have a carbon filter nor a skimmer in my system. It has been running for over a year now but the candy canes were added only recently. I shall also say that I do a 3-4 gallon water change every 2 weeks.
Do you add any additives to your system? Would you recommend me adding anything like trace elemenets? calcium?

Thanks!