Sadly it seems I am back to square one with my frog. He has refused to eat ever since he ate one cricket 5 days ago. Now when I add crickets he doesn't react at all, although I make sure he can see them. I wrapped the tub in black fabric the other night to reduce visibility, but he remains the same. He doesn't seem restless or stressed in that he typically remains half buried in the substrate and doesn't do a lot of moving around unless disturbed, he just refuses to eat. I'm planning to contact my local vet to find out if they have anyone skilled in working with frogs.
I'm starting to think that I must have made some unknown mistake along the way in my care of this poor frog. It's incredibly disheartening for a pet that once had such a strong appetite slowly become thinner and stop growing from refusing food, and knowing that the cause was likely something entirely preventable. I can only hope that this will just be a tough period of his youth and that he'll end up recovering and living a long and healthy life.