I wouldn't worry about dosing any of that. Are you testing for calcium, molybdenum, etc.? No? Then how do you know you are not overdosing your tank? None of that stuff is necessary for a new tank. Don't dose for anything unless you test for it first and find that you need to add it. If you are doing water changes, the salt mix will often contain a correct concentration of all that stuff.
There are all sorts of frozen foods out there. Mandarins would probably prefer something smaller than brine. Try mysis or frozen cyclopeeze.
Mandarins are very tough fish to keep alive in new tanks because of their feeding requirements. They tend to starve to death. In the future you should research the animal before you buy it, and make sure you are aware of its needs and that you can provide those needs.