hello; Perhaps water changes of less volume and/or less often. The purpose of a water change is to keep the water parameters good. Much will depend on the stocking of the tank and to some extent the feeding. Heavily to overstocked tanks may need such large and frequent water changes. Heavy feeding can add to the need for more water changes.
The use of live plants helps as they use up some of the nitrates. I also have gone to lighter stocking densities of fish which helps. I also feed much lighter than before, even to the point of skipping feeding a day or two each week. Some foods are less messy than others as well.
When you get to the usual water change time, check the parameters. Perhaps you will be good for a few more days and may also be able to use less water.
I have a septic system so do not use the old tank water for flushing. On a city sewer it should be fine. I do use the old tank water on house plants and yard plants.
