Pink tail chalceus is a true top water fish as I have never seen mine dive below mid level. It’s not a schooling fish but often recommended to keep either one or a group of 6 to reduce conspecific aggression. I keep one in my 75 and it has zero aggression to other fish. Your 2 meter tank isn’t big enough for 6 as full grown pt can reach 10 inch. My friend kept 4 in a 180 gal tank and eventually reduced to one as they constantly locked jaw and fought one another.