Because Geo pyrocephalis (Rio Tapajos) is a more northen, and " tropical species", compared to Gymnogeophagus balzani, a subtropical species,
I do not personally consider them to be compatible long term, unless you split them up for a temporary cool down period each season.
Lets consider that Sanatarem Brazil (on the Tapajoas river,) is nearly 2500 miles north Bella Union where many balzani are from, near Montevideo Uruguay .
The distance between Miami and Toronto is closer (only 1500 miles),
maybe that seems like apples and oranges, but climatic conditions, and seasonal differences are quite drastic between the 2 areas of S America.
When I first tried to house Gymnogeophagus in tropical temps year round, I ran into fungal and bacterial problems when not giving the Gymnos a winter cool down.
You might also consider Amazonian water parameters in the north can be different than in te south.
Because I have kept both species, but would not keep them together, because pyrocephalus prefers constant temps in the low 80s, balzani would like a winter cool down in the mid 60sF.
My balzani were the Uuguayan Bella Union varient, so If you can access a more northern Brazilian varient, it might be possible.
