I'm frustrated I continually see people recommending it. There is really no reason to do it other than to see if they won't kill each other. Put a divider in that big tank, bam. Two males, no risk. Stop telling people to plant it heavily and put two males in there! Fish release hormones into the tank, and as others have mentioned, two males will hunt each other down. There is no reason to do it, so just don't.
When males work out in tanks together they have been together since they were born or very young and grew up together. Even usually then it doesn't work out.
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