African Dwarf Frog floating on top of tank :(

I recently purchased four African Dwarf Frogs. I put two of the
little guys in my one gallon filtered tank with my Betta. One of the
frogs almost immediately floated to the top (well, after an hour) and
he has been there ever since. I purchased (per various pet store
recommendations) quite the variety of food and found that three of the
frogs will eat frozen blood worms. I have never seen poor Floaty eat
anything, though perhaps he eats when I am not looking. When I
carefully touch Floaty he will move so he is alive. For quite some
time he only floated without movement. Yesterday he was quite active
(for him) and wiggled and swam around. At one point I watched him
attempt a number of times to swim to the bottom, only to pop back up
to the top.

One of the frogs in my other tank also started floating, but I suspect
that I overfed him, which can be remedied. However, I am quite
worried about Floaty. Except for this "stuck on the top of the tank"
business, he seems quite healthy. He is absolutely not bloated.
What's going on and what can I do for him?