Trace elements, suppliments and plankton are all entirely different things. As mentioned, there is no need to does trace elements or additives if you do regular water changes. In fact, it is very easy to over-dose some of these elements which will cause you problems.
Cuz I was planning getting an anemonae earlier and then just feeding it plankton
this is not a good idea. As kat stated, they derive most of their energy from light. You should not purchase an anemone if you do not have the appropriate system to care for the animal. Plankton will do little to help this animal and will only foul your water.