be patient with the yams mine took a bit to get a like for them. Make sure they are anchored to the bottom (try a fork or very dull knife(stainless of course)). Yams seem to last awhile in my tanks without going bad also maybe 2 days max.
mine also like algae flakes, algae wafers, basic flakes,zuchinni, cucumber peeled,romaine lettuce leaves.
make sure they are anchored and not floating floating or only a really aggressive or hungry BN will go after it.
watch out with zuchinni and cucumber as they can turn fast and go bad also maybe 1 day max.
reference at planet catfish also.
My baby longfin and 144 seem to like romaine and algae flakes best.
just edited my post I realized Wheels was right about the time for zuchinni and yam. I tied leaving a yam for 3 days and it didnt look so hot.