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 that you put 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.
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.