The hardest part for beginners who are managing the care of goldfish water temperature.
Fish are poikilothermic animal body temperature changes with temperature. Therefore, abrupt changes in water temperature may shock the fish they will be dead.
So when adding or changing your water, care must be taken prior to temperature and temperature difference. When the water changes I have been at most about half the tank about 3 / 2.
However, the difference in temperature between day and seasonal changes in temperature will be stimulating rather, creates a strong body for the goldfish.Deco sticker Itasha