60x18x24 is a 120. That is what I have
The 72 is a 125 gallon.
You will make the right decisions. You have joined a very friendly and expert board here. Everyone here will help you make all the right decisions.
I am far from an expert, but these guys here have helped me a long way in my knowledge. Especially Noddy, Necro, Nicki-Sue, Paul and OFL. They are all awesome here though. Everyone.
4" IMO is a bit iffy for a CL, still because the fish only has to fit in the oscar's mouth width wise, not length wise, if the oscar nears full growth. I have had my loaches about 10 months and it seems they have only grown like 2-3" (they are slow growsers)
If he can get his mouth around it, it is open game.
My oscars are 9"+ now, and the loaches are about 5-5.5" The oscars aren't able to get his mouth around my loaches at this point.