Anorexia is usually a symptom of a deeper problem, such as improper housing, internal parasites, stress, etc.

I would get him into a smaller enclosure such as a 15qt tub. Get your temps up on the warm side to 94-95, cool side 83-85. Put down newspaper, a small water bowl and a small hide. Leave him COMPLETELY alone for 1-1.5 weeks, and then offer a live medium adult mouse or a rat pup. If he doesn't take it within 5 minutes or so, take it out and repeat the next week.

450g at 1.5 years old is pretty small. I would get his next bowel movement to the vet to have it checked for parasites just in case. If he's clear of those and healthy, then I would honestly just switch him to a plastic tub and put him in a dark, quiet place. He may not be feeling secure enough in the tank.

There's no need to resort to gerbils/asf rats/etc until you fix the husbandry problem and possible health problem(ie internal parasites if he has them).