That lighting is fine for softies. You don't really need to worry about calcium unless you plan on keeping lps corals, your lighting isn't sufficient enough for sps. Before you think about dosing, you should test for magnesium (b/w 1250-1350ppm) and iodine (~.06ppm), those are the most important elements for softies. If they test low, then you can consider dosing, but once a week wc should be efficient enough to keep the parameters in check unless you have a lot of corals. If you keep gargonians, sea fans and the like, you can also test for calcium. I feed my reef phytoplankton everyday and cyclopeeze every other day. It doesn't hurt to spot feed the corals either to ensure all the corals get food, but majority of the corals get majority of their food by photosynthesis from the light, but I would still feed phytoplankton just for extra nutrients.