I have a 10 gallon filtered tank, cycled now for ~2 months, with a thriving java fern and silk plants. It has housed 6 harlequin rasboras until last night when I decided to put my male halfmoon Finley in there. Fin has been living in a 5 gallon tank.
It's been 12 hours and every now and then I stop by the tank to observe the community together. It seems as if the harle's know to stay out of Fin's way. When they get close to him he'll flare, and they'll swim to the other side. I've seen minor chasing for like 2 seconds at a time but the harle's are just way too fast for my big boy.
Fin has found refuge in a log I have in the tank. He'll watch the harle's from the holes, and as long as they're not in his general vicinity he doesn't flare.
Is Finley's flaring a sign of aggression or just defensive? What things should I keep in mind and look for when determining whether this will be a peaceful community?