How Often Should You Water Change a Fish Tank?

One-size-fits-all answers to most questions are rare. How often you should water change a fish tank is no exception. Both water change volume and frequency depend on numerous factors. These factors include stocking density and the fish you’re keeping.

It also differs between freshwater and saltwater aquariums. There’s some good news, though. Because when it comes to tropical freshwater community tanks, there’s a one-size-fits-most answer.

In a typical tropical freshwater community tank, you should change around 25% of the water every week.

Alternatively, doing one larger fortnightly 50% water change may be sufficient. In any case, the goal of performing regular water changes is to maintain healthy parameters for your fish. Performing water changes dilutes nitrates and other pollutants. It also helps to keep your pH in check. Keeping your pH in check prevents it from swinging or crashing.

Siphoning out old water also provides the perfect opportunity to vacuum the substrate. By attaching a gravel cleaner to the hose, gravel, sand, and other substrate options can be agitated and washed in the process. Dirt from the substrate is then cleanly and effectively removed from the tank along with the old water.

For the most part, changing a quarter of the water volume weekly will do the trick. Again, that’s for a typical tropical freshwater community tank. For other types of aquariums, different rules apply. Tanks containing messy species like goldfish will likely need bigger or more frequent water changes.

Malawi cichlids

The same goes for the average Malawi cichlid aquarium. That’s because Malawi tanks are generally massively overstocked on purpose to limit aggression between individual fish. There are further, more specific rules for species like discus as well. Saltwater aquariums and coral reef tanks, in particular, also call for special consideration.

At the same time, heavily planted freshwater tanks may require fewer water changes on average. Meanwhile, big water changes—such as 50% every fortnight—are often a no-no for tanks containing delicate ornamental shrimp. Again, it’s about maintaining a healthy balance for an aquarium’s inhabitants.

Not sure how much water you should be changing? Need assistance with your routine water changes? Drop us a line or read more about our fish tank maintenance service to find out how Your Aquarium can help.