hi i would like to know if it is okay for me to add a koi angelfish with my others fishes like silver angelfish,black ghost knife,catfish and congo tetra? on the other i keep noticing that my cousin's gourami keep on chasing his swordtail fish.can i know how to avoid this to happen again? i am afraid that it miht resulting in the death of the fish as initially one of his guppy were found death after being chased by the dwarf gourami..