At 3 months old it is not a fry, it is probably what we would call a juvenile. It is probably not yet grown to full size but is far larger and more mature than a fry.
Well in my opinion,That depends no how big your frys are now,
i have 4 month old fries of length ____ and ___________. so i think this depends on how healthy your fry are grown.
If you have a fungus on your young fish, they will not recover without help. You must treat the affected fish. If you can safely separate the ones that are affected, you will spare any that have no problems yet from the impact of the treatment. That applies equally to adults or the tiniest of fry.