I generally feed the 1mm NLS pellets. I also try offering the very small Hikari pellets and the BZA food, which has sizes ranging from almost a powder up to small granules (that are smaller than the NLS 1 mm pellets). The yln cruises right up to them and to NLS flakes, checks them out, and then turns away without eating them. It does like live blackworms, though.
Conversely, the falcula will eat the pellets (mostly off the bottom, but a few from the water column) and flakes but isn't at all interested in the blackworms. My ulietensis and saddleback (now in the DT) aren't interested in blackworms either but love the pellets.