:iagree:The only thing I'll add is that for the 20G, unless you're going to breed them, I would only keep one in there. And that one will need to be fed with supplemental food just like any other fish. There won't be enough natural biofilm or soft algae to feed it. Same goes for the 36G....if you're not looking to breed them, just put 1 or 2 in at the most. If they both turn out to be males, they won't fight. It's when there's a female in the mix to compete for that the BN males will fight to the death. They would still need separate cover places and plants to break up the space between their cover spaces. I have 8 or 9 in a heavily planted 75G....it's their breeding tank. I have one mature male and one male approaching maturity in there. I'm keeping my eyes on the boys since the girls are going to spawn soon. I have two caves that are totally out of eye view of each other. If I even suspect that they are competing against each other for the same female....one male will come out of there. And I don't raise any of the fry in that tank. I have a separate growout tank for that.