My bearded dragons are about 7 months old. One is about 13" long (head to tip of tail), very active and eats plenty. The other is only about 5" long (head to tip of tail), eats a little each day, poops regularly, but isn't very active. He often sits on the ground in the same spot for hours at a time while the larger one walks around and climbs the stick, adjusting his position in the tank frequently. They have both been in the same habitat since birth, been eating the same foods, getting water and veggies, are in a tank of about 93-105 in the basking area and 85-90 in the other end of the tank, and getting calcium every other day. They have a power sun light/heat emitter which provides UVB. They also have a 24-hour red light which keeps their tank warm when the power sun goes off at night. Why is one growing normally and the other is still so small?

I'm so worried about my little guy. I don't know what's wrong or why he's not growing like the bigger one.