FWIW, most corals don't actually feed on phytoplankton, but instead on zooplankton (although technically it's mostly a particle size issue I think).
Clams and *some* corals do feed on phyto, but most corals don't. Instead, dosing phyto tends to feed the existing zooplankton population which then may hopefully proliferate more, and thus indirectly benefit the feeding of your corals that way. But you're not directly target-feeding your corals phyto.
Zooplankton on the other hand will have a direct target feeding benefit. Stuff like rotifers, possibly even baby brine shrimp, and so on. Basically, little itty-bitty critters that move on their own, as opposed to free floating plant cells.
Just thought I'd share that little nugget of info.
