Feeding a malnourished Firebelly toad?

[Gnag the nameless]

That concerned me too... a photo of the tank would help. In it's current condition. Not right after you cleaned it, or when you first took a photo of it, but the closest time to when the frog got sick.

I check my frogs a lot. I don't do physical examinations or disturb them, just come out at night and use a dim flashlight, looking under the water to see their underbellies [I also check the water at the same time. A tiny bit green or looking off, and I refresh it ASAP], and look from above to see their backs/heads.

I always get that stabbing, pained feeling when I see unhappy animals at pet stores. The bettas in the cups are some of the worst to see, but hamsters without water and frogs with empty water bowls or really dirty water...