I now have a divided aquarium (used the plastic canvas and report binders trick) and I have just released my two fishies into it.
Slight problem... there is a small gap, a millimeter or two, on the sides of the divider (it's not siliconed in, but held securely in by notches at the rim of the tank) and they went right to it and began flaring at each other :(
Actually I think some of it is them flaring at their own reflections (they do it also when the other fish is on the other side of the tank), or the reflection of the other fish that they can see on the glass through the little gap...
To those with divided tanks, did your fish get used to this eventually??
They're completely new to this tank, and constant flaring is something I did not want in the first while of them getting used to it :(
(How do people with see-through glass dividers do it?)