36x12x18, that's 30 gallons right!
So you have a couple of nice looking males there, I'd personally keep the first fish pictured and return the second male, for three females. Have you seen my sexing guide? It might help you with this.
I would not really advise that you keep a single pair of these fish together, it can and will work for a very long time, but can quickly turn sour. Several females for each male is a good way to dissipate the inevitable spouts of aggression that occur during the courting, breeding and rearing process, not to mention the simple establishment of hierarchy and shifts in the group dynamics that this entails, all very entertaining and much less stressful on a larger group of fish.
In your tank I would keep 1 male and 3-4 females, this will make life much easier and the male will benefit from a selection of genetics etc.
The tank you plan on moving them to, will it have a sand substrate? These fish are very much sand sifters - their name, Mikrogeophagus literally means, small earth eater..... A sand substrate will bring about fascinating behaviour :thumb:.
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