ALW
What works for one may not work for another!
PS just looked up online - the butterfly should be ok in your tank!
Depends on which one.
H. acuminatus - no require 100g
H. chrysostomus - require 75g but could get away with one in 55g
H. diphreutes - require 75g but could get away with one in 55g
H. intermedius - no require 100g
H. singularis - no require 100g