Hi everyone!

Background:
So since getting everyone's advice I've stopped stressing and gave Mochi lots of space. I stopped holding him completely except to clean his cage once. He has a very secure cage and my husbandry has been good. He hides during the day and comes out around 9pm every night and roams around.

I've had him for a month and he has not eaten. The first week and a half I handled him and since then I stopped and haven't handled him since. I had f/t medium adult mice at first that he took no interest in. I tried rat pups that he looked more interested in but never would strike. I'm going back to adult mice, large this time, and am going to have darker ones on hand to see if he prefers that. I've also completely covered the front of his cage with a towel, so now all four sides are covered, and I'm going to give him space until I get the mice this saturday.

My concern:
How much weight is too much weight to lose before I have to take him to the vet? He's 7 months old (I believe) and I'm guessing around 130grams (136g when I last weighed). He's lost around 15g so far and he's just so tiny.

I'm trying the towel thing and then the mice. I'll try live after that. However, at what point should I decide it's too much weight-loss and take him to the vet? (if he continues not to eat).
-concerned madre