Most mushrooms do not eat phyto or zooplankton,they usually just get there nutrients from the water or through photosynthesis as most do not have a gut to digest anything..Some species like the elephant ear mushrooms do eat some smaller foods such as mysis,brine and so on. I would be pretty upset at whoever told you to do this if my mushrooms ended up dying from there suggested way of feeding your corals ! Also remember that a good rule of thumb is lps (large polyped stonys) eat zooplankton of larger sized microns like mysis,brine ,rods original food. Sps (small polyped stonys)eat Zooplankton of a tiny micron size like the reef nutrition oyster eggs. Soft corals like toadstools,colt coral,and finger leathers eat phytoplankton,they also eat by filtering the phyto out of the water column and imo do not like being fed directly.