It's not until the end of that week that he notices he's building mana more slowly, and having more trouble drawing it out again from his storage.
He— knew that would happen eventually. He wasn't expecting it to happen already. Everyone knows the risks of using malia, but—
Complaining about how unfair it is won't make it not true. If he wants to be sure he can respond properly to threats, he needs to either start carrying around mice with him, or start drawing more malia, more often.
He spends half an hour trying to figure out if there's any reasonable way to carry around mice in his backpack that'll still leave them accessible in an emergency before he gives up. (In hindsight it was stupid waste of time, he should've realized it sooner— but that's not helpful.)
(The pair of mice in the tank he goes for scurry away from him.)
This time, pulling malia feels more like turning a spigot than anything else. It flows into him, and for a moment he's unequivocally confident that everything is going to be fine. Then the mouse stops breathing, and he wants more— there's another one in the cage, and its mate is already dead— no. He's not stupid. He's not taking more than he needs to to top up his reserves.
He feels a little less sick. He hadn't even noticed he was feeling sick in the first place.