Hi. I want to keep a GT in my 55 gallon. Can I keep a pair? (M AND F) or only 1? Maybe with some tankmates too?
I would recommend you look at some slightly smaller south American species, of which you could comfortably keep a pair with some dithers in a 55. Blue acaras would be a good choice, the non-electric blue morph looks just like a smaller GT. A 55 is kind of pushing it for a GT for life, because the tank is only 12" wide.
The acaras would have plenty of room and you could do a school of tetras and some bottom dwellers like corydoras as well.