Live phytoplankton and the like serves two purposes. It will feed some corals/general filter feeders as well as feeding the fauna that can indirectly feed the corals as well, copepods, mysid shrimp and such.
The recommended dosage is 5 ml per 15 gal
of tank water 2x/week but I think you would be fine with ˝ that amount. 5 teaspoons twice a week should do it, mabye even less. Keep a look out for increased amounts of film and other nuisance algaes. If you see a dramatic increase, cut back until you see the algaes subside. DT's is a greaat product but it can also make a tank nutrient rich if using more than is needed.