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Water Changes: Can You Do Them Too Often? (Or Too Much)

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As a fish owner, I always want to make sure my fish get the best circumstances as possible. Doing water changes is a big part of that, and I wondered if it were possible to change your aquarium water too often. After doing my research this is what I found.

Can you change aquarium water too often? Do not change water more frequent than once a day. If you want to keep you aquarium water pristine, doing daily water changes is beneficial. Just make sure you know how to do a proper water change. There possibly is more to it than you think.

There are however a few things you should know. Always make sure that the water you are adding matches the aquarium water parameters and never change more than 50% of the aquarium volume at once. Continue to read to learn more about one of the most important aspects of the aquarium hobby: water changes.

Why doing water changes once a day is the maximum

A lot of aquarium owners who like to breed fish know that doing daily water changes baby fish fry is super beneficial for them. This might even be you! So why than do I recommend not doing water changes more often than once a day.

Well, the water that you add to the aquarium needs to mix with the aquarium water. It is almost impossible to add water to the tank that exactly matches the aquarium water. The temperature, pH and other parameters will differ. To see the optimal parameters or to learn what these parameters mean, you might find this article I wrote insightful.

Aquarium fish (and plants to some extend as well) love stability. If the parameters are not exactly perfect but they are stable, your fish won’t mind. In the pH is 0.5 higher than an employee at your local fish store recommended, it is not a problem.

Every time we do a water change, the parameters will fluctuate. This will induce stress in our fish. Just once a day will not be a problem, but more often will not be appreciated by the fish. It can lead to excessive stress and possibly even deceased fish.

How to safely do a water change

Water changes causing stress is obviously not what we want. How can we reduce stress to aquarium fish while doing a water change? There are a couple of things you can take into account that will cause less stress.

Tip: your best friend while doing water changes is a siphon. You can use a gravel vacuum to siphon water while cleaning your gravel at the same time. I always recommend this affordable gravel vacuum on Amazon. Check it out, you will not be disappointed.

Removing water

A rule of thumb is to never remove more than 50% of the aquarium water at once during a water change. Why is that? Well… there is a risk of destroying the beneficial bacteria that live in your tank. These bacteria help break down ammonia into less toxic products.

If you would for example do a 100% water change (again, never do this) there is a high chance that you deprive the bacteria with food for too long, which kills them.

Another reason why over 50% is too much, is that the shock for the fish increases when you alter too much of the water parameters at once. Changing water parameters causes stress. This can even be the case when there is an extremely high concentration of nitrate that has been building up over time due to a lack of maintenance. This is also called “old tank syndrome”, check out this article I wrote if you want to know if your tank has old tank syndrome.

For effective (daily) water changes, remove around 25% of the water at once.

While you are removing water, make sure to vacuum the bottom of your tank. Sadly for us, there is no fish who eats all the poop from the aquarium, we need to do that our selves. Some people will add a “clean up crew” of fish to help clean them, but know that they are by no means a substitution for maintenance.

By vacuuming the gravel, you will be able to remove all the fish poop, uneaten food and organic plant matter that has accumulated on the bottom of the tank. This is super important and makes for a great water change, as it will start to rot when not taken care of. You do not want another ammonia source in your tank, as this will kill your fish.

Adding new water

In theory, you want the water you add to your aquarium to exactly match the aquarium water.

To do this, make sure you use a pre-treat to treat your tap water. This will remove the chlorine and chloramine in your tap water to make it safe for your fish. I have written an article on removing chlorine and chloramine in the past. Here you can learn more on why, how and with what you should treat your tap water.

The second parameter you can easily control is the temperature. You want the water you add to have the aquarium water’s temperature. To be honest, I always guess what feels right. If you want to be more precise, you can measure the temperature in the bucket with a thermometer.

When you add the water to your aquarium, make sure you do it gradually. This can be done by setting up a siphon that slowly transfers the water from a bucket to your aquarium.

If you add the water all at once, you will notice that the substrate, plants, ornaments and fish in your aquarium are heavily disturbed by the sudden strong flow in your tank. Also, when the water parameters do not exactly match the aquarium water the shock will be rather sudden. Again, this causes stress to your fish.

What is the purpose of a water change

Whenever you are doing water changes, you are removing waste from your fish from the aquarium and replacing it with clean, fresh water. The waste can come from rotting plants, uneaten food or even deceased fish.

The main source of waste are your fish, they produce ammonia which is toxic in low concentrations. Ammonia is converted to nitrite, which is converted to nitrate. Nitrate is less toxic in low concentrations, but when you allow it to build up it will become toxic and cause stress to your fish. This is what you are removing: nitrate.

And yes, you can add live plants to your aquarium that help you clean. This is actually a rather good plan as they also look beautiful and provide cover for your fish. I even wrote a complete article about this so I am not going to go in too much detail here.

Removing this nitrate will make sure the water stays safe for your fish to live in.

My Favorite Fishtank Products to Make Life Easier

I am so happy you enjoy this post so far! You will also definitely like my product recommendations that will make your fishkeeping experience so much better. I’m 100% sure you’ll love them! Check them out here:

1. A good gravel vacuum; Without a gravel vacuum, cleaning the substrate of your tanks is near impossible. Whenever I want to remove some of the sunken detritus from the bottom of my tank I’m happy I’ve got one of these. Click here

2. Liquid plant fertilizer; It’s no secret that I do not like nutritious aqua-soil. It makes a mess and only works for a given amount of time. Instead, I always use a liquid aquarium plant fertilizer. Everyone who keeps live plants needs it, it’s not that expensive and makes your plants grow better. Click here

3. A set of aquascape tools; I love keeping plants, but planting and reorganizing my aquarium was difficult until I got a set of these tools. It’s much easier to plant any kind of plant compared to using my thick fingers. Click here

4. A liquid-based water test kit; ever since I’m able to accurately test my water parameters, keeping fish became less stressful. Before I was always stressed that my water parameters were wrong, but with a kit such as the API Master kit, I can measure this. It really is essential to successful fishkeeping. Click here

5. A digital thermometer; the more you know about your aquarium, the better! Temperature is crucial for the health of your fish. A thermometer will also show you whether your heaters are still working correctly. It will give you more insight and more peace of mind. Click here


To conclude, yes you can do too many water changes. If you do more than 1 water change per day, your fish will experience unnecessary stress. This is because the water parameters are fluctuating.

Instead, if you really want to do the maximum number of water changes, stay at one water change per day. Never change more that 50% of the water at once, as this can kill the beneficial bacteria in the aquarium.

Related Questions

What is the normal amount of water changes people usually do? Most people do a weekly or bi-weekly water change where they replace 25% of the aquarium with fresh water. This will make sure the water remains healthy and there is no excessive nitrate build up.

What is the lowest number of water changes you can do? If you plan correctly and add a lot of live plants to your aquarium, you can do water changes just once per month. This is because the plants will remove some of the nitrate from the water. They theoretically might be able to remove all of the nitrate, but a build up of nitrates is dangerous. This is called old tank syndrome.

Feature tank image – Author: Emilia Murray Licensed by CC2.0 No changes
Water change image – Author: osseous Licensed under: CC2.0 no changes

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