What water temperature suits ranchu goldfish?

Ranchu goldfish prefer 23–27°C with stable temperature; if it’s too low or high they lose resistance, refuse food, and may die in large numbers. When changing water, replace only 1/3 at a time, keeping old/new temperature difference under 2°C to avoid sickness. Ranchu like weak-alkaline old water, so keep pH at 7.5–8.5.