The next two methods of a water change are both acceptable practices but not without some debate.
- The main argument in opposition of a complete or large percentage water change is that you should not change all the water in your tank in one cleaning because it will change the chemistry of the water too much and will stress or kill your fish.
- The main argument in favor of a large change is that you don’t eliminate all the waste in your goldfish tank with a partial water change and over time the waste levels can build to unhealthy levels.
Both schools of thought are correct; both can cause problems for your goldfish and both stress the importance of having fresh clean water in your goldfish aquarium – So what do you do? Typically, most advice found on the internet says to change at least 20-30% and to never change all of your goldfish tank water during routine maintenance. If you do 20-30% water changes your waste levels will build up but it won’t likely kill your goldfish. They would of course be happier with a larger water change so if you are feeling guilty, up your tank water change to 50-75%. This will eliminate much more waste and by leaving some water in goldfish aquarium, will not drastically change the chemistry of the water.