My suspect why your gold fish keep on dying is perhaps :
1. May be you bought the gold fish that already infected by disease.
2. Your water in the aquarium has high PH (high chlorine).
3. Your aerator is to small enough to supply oxygen.
4. Over feeding will weaken the gold fish.
5. When you transport your gold fish from pet shop to your home - most of the gold fish suffer stress and cause to the gold fish to weak or exhausted.