Why is my guppy fry sticking to a corner of the tank?

I have 2 tanks, a big one for all my fish and a small one for guppy breeding... about a week ago, 2 of my guppies gave birth the same day, leaving me with about 35 baby guppies, which i kept in the small aquarium. about two days later, the big one had a big ammonia spike that killed almost all my fish (lesson learned) so i cleaned up, made a full water change, and set it up again with 3 small fish and the guppy fry. Everything seems to be fine, but this morning i fount about 14 baby guppies huddled up together in a corner near the surface. they all seem to be healthy, but they're not in their usual curious-explorative attitudes. This is my second guppy fry ever, and the first had only one survivor so I don't know if this behavior is normal. Help?