I have had Sveni, Sp. Pacaya and Sp. Belly Crawler spawn multiple times in 36" x 18" x 18" tanks, that would be 50gal or so. I have done an absolutely GIANT pair of "Lepidota" (12"+ male) in a 48" x 18 x 18 75 gal. No problems with either, as long as they are bonded. . . Never lost a female in the process, I have had females kill males after spawns though.