African Dwarf Frogs are known to typically have poor eyesight - and tend to be bottom feeders. The pellets are created so that they will sink.
On occasion, one frog may have a keener sense than the other.
We recommend adding an additional day of feeding - feed three times a week, two pellets per frog. If you still see one eating more than the other, add up to 6 pellets in per feeding (instead of the 4 pellets per feeding in our instructions). Six pellets will not disrupt the chemistry of the BioSphere. This should allow for extra for your second frog. These pellets are high-protein - and optimized for frogs! It only takes one pellet to provide sustenance for African Dwarf Frogs. Watch for any uneaten food. Please remove it with a turkey baster (water extraction tool) after 24 hours.
Like most critters, frogs grow differently. Some wider, thinner, thicker, longer. It is easy to assume that a "larger" frog is eating more than his/her BioSphere mate.
If one frog is truly lacking adequate nutrition, he/she will regularly nibble at the other frog.