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How often should I change the water in my aquarium?

Change the water, image of an aquarium getting it's water changed.

Maintaining a healthy aquarium is all about balance and consistency. One of the most crucial yet confusing aspects of keeping an aquarium is knowing how often to change the water. Whether you’re a beginner in the hobby, or a seasoned hobbyist, this guide will unravel some of the mystery and provide you with an easy-to-follow guide, tailored to your specific aquarium needs. Let’s “dive” into the importance of water changes and how to do it properly.

Table of Contents

Why Is It Important to Change Aquarium Water Regularly?

Regular water changes are essential for the health of your fish. Fish produce waste (poopoo), and even with a great filtration system, toxins like ammonia and nitrites can easily build up in the tank water. And, over time, these toxins can stress your fish out a ton, which leads to inevitable illness or even death. Water changes help rectify all that. They help to remove then dilute these harmful substances, making the aquarium an overall more livable space.

However, beyond removing toxins, water changes also replenish essential minerals in the aquarium. This helps maintain the right pH balance in your tank, gives your snails healthy shells, your shrimp good molts, and plants with lots to eat. Without water changes, over time, the water in your aquarium can become depleted of all the minerals that fish need to stay healthy. Adding fresh water into the tank reintroduces these vital elements back into the tank.

How Often Should You Change Aquarium Water?

The frequency of water changes depends on a few factors. But a good rule of thumb is to change 10-20% of the water every single week. This frequency helps maintain a stable environment, prevents toxins from building up, and adds minerals on a regular basis. If you’re one of the few aquarium keepers with a lightly stocked tank, or maybe it’s heavily planted, you might be able to extend this schedule to every other week.

If you are feeling hesitant or unsure, start with weekly water changes and adjust from there. This is where good water testing comes into play. Keep an eye on your water parameters and your fish. If you notice cloudy water, high levels of ammonia or nitrites, or slow fish, it might be time to increase the frequency.

What Factors Affect How Often You Should Change the Water?

There are several factors that help determine how often you need to change the water in your aquarium. These factors are:

  • Tank Size: Small tanks need a lot more frequent water changes than larger ones. This is because they can quickly become polluted (less water means less stable).
  • Stocking Levels: It’s simple, the more fish you have, the more waste they create. A heavily stocked tank needs more frequent water changes than a lightly stocked one.
  • Type of Fish: Some fish are just plain messier than others. For example, goldfish produce a ton of poo, so their tanks need more frequent cleaning. Pleco are funny too, because they clean a lot of the uneaten food, algae, and plant waste, but they are also poop machines.
  • Presence of Live Plants: Live plants help absorb some of the harmful toxins in the tank, so aquariums with lots and lots of plants might need fewer water changes. This also goes for floating plants, they help a lot too.

How Does the Type of Aquarium Impact Water Change Frequency?

The water type of aquarium you have also affects how often you should change the water:

Freshwater Aquariums

For most freshwater tanks, changing 10-20% of the water weekly is the ideal goal. This keeps the water clean and the fish generally healthy. If your tank is lightly stocked or heavily planted, you might be able to stretch it out to every two weeks. But, when in doubt, change it out. It is always better to do more frequent water changes, especially in the beginning.

Saltwater Aquariums

Saltwater tanks tend to need a bit more care and attention. I recommend changing 10% of the water every few days (like 3-4). More frequent, but smaller water changes help reduce any shock that may result in the new water being added. Saltwater fish and corals are more sensitive to changes in water quality, so regular water changes are crucial.

Nano Aquariums

Nano tanks (those under 10 gallons) require special consideration. They can get dirty and mucky very quickly, so it’s best to change 15-20% of the water every three days, or twice a week. It might seem like a lot, but your fish will be grateful! After all, who wants to breathe their own feces and fluids?

What Is the Best Way to Change the Water in Your Aquarium?

Changing the water in your aquarium is pretty simple to do, but there are a few steps to follow to do it properly:

Tools You’ll Need

Performing a Water Change

  1. Test the water: Before you start, test your water for ammonia, nitrates, and pH levels. This gives you a baseline to start from, and it’s a good idea of your tank’s current condition.
  2. Prepare the replacement water: Fill a bucket with tap water and add some Seachem Prime to remove harmful chemicals. IMPORTANT: Make sure the new water is the same temperature as your tank water. You can do this by regulating the temperature as it comes out of the tap, by letting it warm to room temperature (if your room is warm enough), or by placing an aquarium heater into the bucket. I usually get it right out of the tap. It doesn’t have to be exactly right on for most fish, but some sensitive fish may care more about a degree or two than others.
  3. Siphon out the old water: Using the siphon, remove 10-20% of the water from the tank. Be careful not to disturb the substrate too much, unless you’re also using this as an opportunity to clean it. I usually use two of the same sized buckets of water for my new and old water. So, I have a 5-gallon bucket of new water waiting, then I use a second 5-gallon bucket to remove exactly 5-gallons. That way I don’t take too much or too little out of the tank.
  4. Add the new water: Slowly pour the new water into the tank, making sure it doesn’t stir up the substrate. You can do this by defusing the water with your hand as it goes into the tank, or you can put a glass bowl at the bottom of the tank to absorb some of the waters pressure, or, and this what I do, I put a chair on the table where my tank is. Then I put the bucket on top of the chair, and I siphon the new water from the bucket into the tank. This method is the least disruptive to the inhabitants of the tank.
  5. Test the water again: After the new water has been added in, test the water a second time to make sure everything is a safe range for the fish.

What Are the Common Mistakes to Avoid When Changing Aquarium Water?

Even though water changes are fairly simple, there are a few common mistakes that can harm your fish:

  • Changing too much water at once: Removing too much water can stress your fish out. Fish really prefer stability, and a dramatic change in water temperature or parameters can throw off their whole environment. Or, you can upset the balance of your tanks nitrogen cycle, which will be a bad day. Stick to 10-20% at a time.
  • Not using a dechlorinator: Tap water contains chlorine, which is deadly to fish. Always use a dechlorinator when adding new water. If you do forget to add it before putting the water in the tank, don’t worry, just add some directly into the tank. The dechlorinator won’t harm the fish, and it will remove what it’s supposed to.
  • Skipping water changes: Skipping water changes can lead to a build-up of toxins in the water, like nitrates. Which can be detrimental to your fish, but it can also lead to other nasty things, like algae outbreaks. Consistency is key to keeping your fish healthy.

Remember, regular and consistent water changes are one of the best things you can do for your aquarium. Your fish will be all the healthier, your tank will look even better, and you’ll enjoy your aquarium more.

If you’re looking for maintenance tips, check out recent article on Best Aquarium Maintenance Practices.

Have some questions or tips of your own? Share them in the comments below, and let’s keep the conversation rolling! Whether you’re a new aquarist or an experienced hobbyist, finding the right water change routine will make all the difference. Trust me.

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