not eating usually means stress ... stress usually means poor water condition.

Quick fix ... change 50% of water daily for 3 days.

day 1: after changing 50% water, 50% old water, 50% new water
day 2: after changing 50% water, 25% old water, 75% new water
day 3: after changing 50% water, 12.5% old water, 87.5% new water

Might want to observe belly bloat, and its waste and body for anything unusual. If yes, go to fish shop and get some medication.