I recently rescued a tadpole from a store that was going to flush it because they could not sell it. I already had a cycled aquarium that I had intended to use for guppies, so I brought it home and it perked right up.
It has been identified as either a green frog or american bullfrog, and is about 1.5 inches long. Lately, however, s/he has started becoming lethargic, not eating as much, and this morning I noticed it is getting pale. In fact, I thought it had died several times due to not moving for hours and only moved when I tried to scoop it out, assuming the worst.
I have had it for a week, been feeding pleco algae-enriched wafers, boiled lettuce, and once in a while the squashed innards of a thawed pea. The tank is at room temperature, which is always in the upper 60s/lower 70s. I also have a CFL light on a 10/14 cycle, and do frequent small water changes (just enough to siphon poo out of the gravel. Readings are 0-0-.25.

Is my tadpole just getting ready to go through metamorphosis, trying to hibernate, or is it sick? :/