At the end of the day, who really cares what the "minimum" tank size is for anything? IMO there is nothing "monster" about cramming the biggest possible fish into whatever size tank you have, be it an oscar in a 55g or a RTC in a 300g. We owe it to the fish we take on to provide the best possible housing and provide them with room to grow to their potential maximum size, regardless of whether or not they eventually reach it.
I'd love to hear what peoples recommended minimum tank size for Geophagus altifrons is.
I know mine are probably an extreme example, but watching my group of five that are still nowhere near full grown (around 5-7" now) in a 240x120cm footprint 2000L tank compared to when they were in a 140x65cm footprint 400L tank is night and day difference. I could have probably hosed them in the 400L tank "for life", and I'm sure some people would suggest even smaller tanks, but there is a big difference between surviving and thriving. Seeing them have space to roam and forage naturally makes them far more interesting to watch, the occasional squabble breaks out and they have room to go their separate ways, then they regroup again when food is offered or something spooks them.
It makes me sad thinking that one day my black aro will be one of those fish who have "maxed out" their tank, and I'm still not entirely sure what I'm going to do when it starts pushing 30"+. Even sadder is thinking of the number of silver aros sold at LFS all over the world every day that will never make it into a tank as big as mine.
