I got some maximas recently from barry that came in with aiptasia on the shells. I used some kalk mixed into a thick paste to get rid on them. I just mix the kalk up thick, pull it into a syringe, turn off system pumps and squeeze it on the anemone. Just be sure not to get any on the mantle and you will be fine.
FWIW, Fatherree also states studies that show, although phyto was injested by clams, their fecal matter showed that a large portion of this came out undigested. It may not be the case all the time, but I would be willing to bet the benifit of adding phyto to your tank for the clams alone is a waste. I feed my SPS oyster eggs, and AFAIK there may be no benefit but I do it anyhow so to each there own. I personally, along with many many reefers have kept clams for years on end with no phyto feedings and these clams thrive. I would put my preference on keeping my clams in a tank with good water quality, with correct balanced CA, ALK, and Mg. JMO/E........