As fish and other organisms live in your aquarium, they naturally create byproducts (like nitrates) which pollute the aquarium environment. Various filters can improve the water quality, but as pollutant density increases, you’re ultimately fighting a losing battle. Eventually, the water in the tank will need to be replaced in order to maintain a clean and good-looking aquarium.
The biggest mistake you can make as an aquarium novice is thinking that in order to replace the water in your aquarium, you have to remove all the fish, drain the entire aquarium, and put new water in.
You see, some of the chemicals and biological organisms in the water are actually very beneficial to the aquarium’s inhabitants. As they live there, the fish in your aquarium create a balanced ecosystem that allows them to thrive. If you were to replace all the water at once, your fish could actually go into shock and die because of the radically different chemistry in the tank you’d be throwing them into.
The solution? Partial water changes. A partial water change involves replacing a minor portion of the water (usually in the order of 25%-33%), which allows you to dilute the pollutants in the tank while still retaining a lot of the same chemistry, thus keeping your fish comfortable.
This is also a perfect time to vacuum the gravel to remove debris such as fish waste and excess food.
The amount of water you should change and the frequency of these changes really depend on the fish load of your tank (the density of fish relative to the volume of the tank). Instead of relying on trial and error, you’re better off asking an aquarium professional to do the first few partial water changes and then suggest a schedule for you to follow going forward.
Don’t hesitate to reach out to Blue Planet Aquarium if you have any questions about water changes in your tank. It’s better to play it safe than risk the well-being of the aquarium inhabitants!