Fish 101: The Importance of Water Changes

Keeping fish can be intimidating at first. Care requirements range from very simple to mind-boggling depending on the type of fish you have. Regardless, one regular action you'll need to take is doing partial changes of your fish's water. 

The fish we keep in aquariums evolved to adapt to their natural environments in lakes, rivers, and oceans. All natural bodies of water have a constant influx and outflow of water and nutrients. But, unlike wild environments, our aquariums are not self-sustaining ecosystems. They aren’t large enough to contain everything that would feed the fish and take care of their waste in the wild. The animals and plants in our aquariums can’t survive without outside help. Everyone knows that you have to feed your fish, but regular water changes are just as important.  

Silent Killers: Nitrates and Phosphates In Aquarium Water

Nitrogen Cycle infograph

The main reason that we do weekly water changes is for something that we can’t see: to remove excess nitrates and phosphates from the aquarium. Nitrates and phosphates are natural nutrient by-products of fish waste, uneaten food, and decaying debris (like dying plant leaves). They are fully dissolved in the water so we can’t see them, but they will continuously build up in an aquarium until they are physically removed by a water change. While both nitrates and phosphates are fine in small amounts, at higher levels they can cause a lot of algae, and more importantly they can make your fish very sick. 

Essential For Life: Trace Elements In Aquarium Water

Tap water has trace elements that fish need to stay healthy, which they absorb in small amounts over time. These essential trace elements for our fish include Iodine, Molybdenum, Vanadium, Nickel, Copper, Cobalt, Manganese, Iron, Selenium, and Zinc.  When we replace the dirty water with fresh dechlorinated water, we are also replenishing those trace elements. Fish that don’t have access to those trace elements generally don’t get sick right away, but it will affect their immune system and other vital functions. It’s a lot like a person with a vitamin deficiency – it happens slowly and isn’t noticeable for a while. Then suddenly, it’s obvious that something is wrong. 

Keeping It Clean: Removing Waste & Algae From Aquarium Water

Cleaning gravel with a syphon

Water changes are also a great time to keep your tank looking beautiful. When you do a water change, you can also remove any accumulated waste from the gravel in your aquarium. Cleaning the gravel will also help with nitrate and phosphate removal. In addition, you should remove any algae that’s on the walls or décor, trim back any live plants that have grown too large, and put the decorations in their proper places. Doing these little actions alongside your water changes will help your fish live their best life.

Being Aware: Monitoring Your Fish During Water Changes

A group of tetras

Finally, water changes are a great time to observe your fish closer than usual. How are they behaving? Are they colorful and vibrant, or are they looking a little dull? Do any of them have weird spots or abrasions? Are there babies in there that you never noticed? Are anyone’s fins a little frayed? Is anyone hiding in the corner or generally acting strangely? Fish behavior is fascinating, and small changes can indicate whether they are very happy, starting to get sick, maturing into adults, or any number of other things. The whole reason we keep fish is that they are really interesting and beautiful, so taking an extra five or ten minutes to observe them is another great reason to keep up with your weekly water changes. 


As you can see, your fish get a lot of benefits when you change their water. That’s why weekly water changes are the most important thing you can do for the health and happiness of your fish. And the best part is that doing a water change is quick and easy. The overall concept of the weekly water change is so simple: you remove dirty, gross water from your aquarium and replace it with clean tap water that you add dechlorinating drops to. For smaller tanks (20 gallons or less) it often takes 15 minutes or less. 

If you have an aquarium or are thinking of getting one, a weekly partial water change should be part of your routine. It’s fast and satisfying, and it is the biggest contributor to having happy, healthy, beautiful fish.