Hi there.
I have one African dwarf frog, but don't worry we are planning on getting more. we got another, but his brother died and the water quality was fine and I made sure everything was perfect, he died the day we got him so I don't think it was our fault. the death of his brother is unrelated, but anyway, we have smooth pebbles as substrates that are large enough for the ADF to not swallow. the issue is I almost feel like it may not be the right one since I have been trying to feed him and the pellets sink in between crevices or deep under the pebbles and I am worried about it. I have hand-fed him bloodworms though and that is going fine. I tried putting a small glass dish down for the pellets to be on a smooth surface so they wouldn't sink. however, this might not be the best dish since he still isn't able to eat from it. I am pretty sure Glass is aquarium-safe.
Any suggestions?