I feed my discus 3 times a day and the amount of water change I can do is 30 percent. How can I get the best result by doing 10 percent water change after each feeding or 30 percent after last feeding?
The main reason to change water is to keep water quality constant and good.
If the water quality is stable and good, there is no need to change water often.
After feeding the water quality will be affected by the left over food and the waste of the fish. Both will pollute the water, so changing water is necessary.
If you have a filtering system to manage waste (ammonia) from the fish, then do not overfeed so that there will be no left over food to decay at the bottom of the tank. You can then do less water change and only do it to remove left over food.
The best time to change water is after feeding.