We are still having issues. I can't figure it out. Our frog is acting sick again, floating at the top. Typically, he just floats with his legs hanging down, but now it seems like he's having a hard time keeping his legs from floating up to the surface, so I'm very concerned about him. He's pretty lethargic, too. He shed a lot of skin yesterday and was very frantic about trying to get it off. His coloring seems to have gotten darker as well.
I have left the tank alone for about a month now. Just 25% changes every week or so. Ammonia is still crazy high. Yesterday, for fear of my frogs health, I did a 75% water change and after the change, the ammonia was still at a 4! No nitrites, but high nitrates as well. How do I control this? Using an established tanks sand doesn't seem to have worked.

Is my frog just a major ammonia producer? I've been trying not to feed him much, but I also don't want him to starve. He was moving around yesterday trying to eat the pellets I fed him.
What would cause high ammonia and high nitrate, but no nitrite?