Well, as for too many minnows comment bro, I have the same issue with those foam buckets. I buy 3 dozen and within 10 minutes, half of them are dead.

I never go higher than 2 dozen. But they are right. Too many fish in a small tank won't work. Think of it as like a home fish tank. You have a 20 gallon tank and you don't want to put more than 10 in there. They will need more swimming space. Fish are territorial as well, so you don't want 100 fish in there.