Suplements for these corals?

I have read that some of the corals I have need supplements added to the water (ie, calcium, strontium, trace elements). Through another post I made here I'm learning that I should not need to supplement anything if I do reg water changes with a good salt mix. I do a 5 gal water change with Oceanic Reef Crystals every other week and was wondering if any of these specific corals need to be supplemented. I feed a capful of Julian Sprung's Marine Snow every other day (a mixture of cultivated phyto plankton and zooplankton). Do I need to add any other supplements? I HAVE researched these, but I'm getting different answers here than I have gotten elsewhere and I find you guys to be more accurate usually. Here's what I have...

I have a 29 gal biocube, all in one system with LR (about 30 lbs), LS, no fish right now, 2 cleaner shrimp, 1 emerald crab, 12 dwarf blue legs, and 6 astrea snails. My corals are 1 fox coral (6inch wide, 3inch tall), 1 pink hammer coral (Heads measure 5 inches across total), 1 pink & purple open brain (about 3 inches across) 1 purple gorgonian, aka purple sea plume (8 inch tall, 4 inch wide) 4 mushrooms, and about 9 white feather dusters that I didn't buy, they just kinda "showed up" one day.

 

You should be okay with just water changes, but if you are serious about corals you should be testing for cal, alk and mag. These are the big three and for corals to thrive they should be kept in balance. Once testing for these 3 you can dose to maintain their optimum levels. You may need to dose cal and alk, but mag should be good with water changes. Never, ever, dose for anything you are not testing for. As far as trace elements go you need not be dosing them, water changes will cover that.