you want at least some flow in the tank to push the phyto around and make it available to everything. It seems more natural to have flow and food available at the same time. Shutting off your skimmer for a few hours after feeding planktons will help avoid wasting any. Mechanical filters such as sponges, floss etc. will do nothing to the phyto. Phytoplankton generally is too small for it to get filtered out that way.