the biggest bleeding heart tetra i have ever seen was by itself most of its life. i had it in a 55 with assorted other fish over time, but it never had a school. many times fish will 'thrive' when under what really isnt considered ideal, but that doesnt make it okay. in fact many times when things are changed to the ideal conditions, you see how 'thriving' was really just really good. and true thriving should always be the goal. and single incidents should never be cited as support to do things varying from ideal.