If the pellet didn't float back up right away your RES likely ate it. It's possible your RES didn't see the second pellet.
One thing I have noticed about the RES that I am pellet training is that they don't seem to see very well when food items are above their head and slightly in front of them. They always seem travel 15-20" or more straight out in front of them to eat something off the surface. This includes bloodworms on the surface which they love to eat. This might be one of the reasons they are hard to pellet train and prefer to hang out in deeper water. Their visual acuity and behavior seems to be geared for feeding on items below them rather than above.
