As long as it is to raise fish, it is to move water. No matter koi fish or other fish, koi fish is a kind of swimming fish, which is a good moving water. As for the quantity and color of geomantic omen, of course, it is exquisite, but it has little influence, has little to do with it, and is not necessarily different. I have a feng shui fish, so I will make up one right away.
Your room is small, so you shouldn't keep koi fish. Just choose some fish that often swim, and the species is up to you.
The bedroom is a resting place, so be quiet and don't move, so don't put the fish tank in the bedroom.
As for the fish tank, where should it be? It must be placed in the prosperous position, but if you want to find a prosperous position, you must set up a house to sit on and start the astrolabe. Not every house may have a prosperous position suitable for putting fish tanks.