Trimacs will be fine in a 75 for at least a year or two as a pair and maybe up to 3 years for single specimen. A 120-125 is more ideal for permanent. I say get a small group and grow them out in 75 and keep a small pair. But keep in mind that they can and may be rough on each other and as they mature and grow the chances of the male killing the female increases. So you might end up with a show male in the long run
plus they are very hardy fish too. I've got a small pair in a 75 now as well and they're doing fine
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