We have huge stock tanks (300 gallon), and the fish seem happy enough. I’ve only had one die in 2 1/2 years. Without fish, the top of the tank is covered in mosquito larvae within two days.
Dumping a tank of that size weekly is not practical. Having a huge volume of water to work with ensures that there is always enough water in summer and seems to be enough for the fish.
My mare is in with fresh buckets at night, and usually the first thing she does in the morning is head out to the fish water for a nice drink.