A pearl goldfish. One of them should be all black, two all red and one purple. Anything else? Black, full red and purple goldfish had better be as big as others and bigger than others. Remember to put it south, and the upper left corner is after entering the door.
The position of Qinglong (that is, facing the upper left corner of the fish tank) can also be changed to 2-day beads, 2 tiger heads, 1 beads, 2 phoenix heights and 2 lions. If you don't know anything, you can look at the flying blue whale and the quintessential goldfish.