Personally, I think the fish tank should be placed in an auspicious position in the living room. This auspicious location is different in every family's house. Find this auspicious location first, preferably a more conspicuous location in the living room.
Let me start by saying which points should not be put.
The fish tank faces the dining table, which is the place to eat. Facing the dining table with the fish tank, it has the feng shui function of making money, which is similar to that of fish.
The fish tank can't face the gate. In this way, there is a risk of wealth dispersion, and the wealth of the fish tank will be dispersed as soon as it opens the door. I have seen many fish tanks placed at the door as screens before to prevent people from seeing the living room directly and play a role in shielding.
Fish tanks can't be placed under idols. In this way, there is a saying in Feng Shui that "put the righteous spirit in the water". This is a bad influence with the meaning of breaking money.
It is not advisable to put a fish tank behind the sofa. Fish tanks are filled with water, sofas are used for sitting, and water is unreliable. This metaphor is not good either.