The plot thickens............
Truth be told ALL Payara are difficult. A lil' advice - if you buy any payara make sure the tank your putting them in is full matured, been running stable for a year or more.
They are very sensitive to water quality issues and easily stressed from transport.
At 3" I'd use a 55 gal for only a few months and the payara would be solo. After a few months upgrade to 75 and add 2-3 tankmates after 6 mo. upgrade over 100 gal.
and slowly add more tankmates.
There in lies the problem see.......................55, 75, 100+ all cycled and fully matured within the 1st year, that's how I've done it, not sure how ppl have those options. Granted if you have a 100+ fully matured you could drop him right in but who wants a big tank with one lil' fish. And if you think I'm crazy - try a Saltwater tank and you'll see how important it is for tanks to be fully matured.
Obviously from the overwelming responses you have gotten to your question I'm probably not typing outta my rear end.