Aquarium Water Changing: A Guide

aquarium water changing@LuqueStock / Freepik

How often do you tidy up around the house?

If you’re like most people, it’s probably not quite as often as you’d like. But you do what you can when you’re able. You try to keep your carpets vacuumed, your counters cleared off and wiped down, your sink empty of dirty dishes, and your trashcan from overflowing. And yet, it often seems like it’s never enough. There’s always another floor to mop or toilet bowl to clean.

And you know what would happen if you just let it go – an unhealthy and uninhabitable environment.

Although you may not think of it in the same way, this is the reason you need to change your aquarium water on a regular basis. Your aquarium is an entire mini ecosystem for your aquatic pets. It’s their home. And if it becomes filthy and uninhabitable, they can’t simply walk outside and get some fresh air.

They’re relying on you to keep their home fresh and livable. And whether you have a fresh-water or salt-water aquarium, learning the whats, hows, and whys of aquarium water changing is an absolute must.

So, let’s dive right into this important topic!

Why Do Aquariums Need Water Changes?

Your fish or other aquatic pets spend their entire lives in your aquarium. And over the course of weeks and months, their healthy water can grow stale and even dangerous.

Unlike in their native habitats where the larger area allows water to be easily recycled and toxins to be diffused, your aquarium is a closed space. And though effective water filtration systems can help your water last longer, they can only do so much. Eventually, your water will have to be changed.

why do aquariums need water changes@alexkoral / Freepik

This is because chemicals are constantly being introduced into your aquarium. This takes place through feeding, conditioners and other supplements, and the natural metabolic processes of your fish or other aquatic animals.

Just think of the food that winds up on the floor of your aquarium uneaten. Like food that’s left out in your kitchen, it will decay. And your fish release waste like any other animal. All this waste and decayed material adds up over time. And that doesn’t even take into account the fact that your aquarium’s water needs certain minerals and trace elements for the good of your pets. These things can be used up over days and weeks, leaving your aquarium’s water with an unbalanced pH.

And while a filter can help balance water over the short run, it’s not a panacea. There will inevitably be a slow build-up of chemicals that can negatively impact water quality and, subsequently, the quality of life for your pets.

And don’t think that this only applies to freshwater aquariums. Saltwater aquariums are just as susceptible to the same negative effects of leaving water unchanged over the course of weeks and months.

Just consider the following negative effects: 

Nitrate Waste

Your fish release ammonia through their natural digestive processes. That ammonia is then converted into nitrites and nitrates by filtration systems. And those nitrates can quickly accumulate, creating an unhealthy environment for your animals. Dangerously high levels of nitrates will stress your fish, making them more likely to get sick and lowering their overall health. It can also do major damage to any invertebrates or coral that may be living in your aquarium. The best way to maintain healthy levels of nitrates in your fresh or saltwater aquarium is simply by changing the water on a regular basis.

Decaying Organic Material

As we’ve already noted, organic material such as food and waste can build up in your aquarium, even if you have an effective filtration system in place. This organic material will break down and disperse throughout your aquarium, leading to cloudy, dirty water. If you have any coral or invertebrates, they need clear water so they can get the energy they need via photosynthesis. But if light has a hard time making it through your murky water, they won’t be able to. In addition to these problems, decayed organic material can affect your water’s pH which is especially dangerous for saltwater aquariums.

A Lack of Essential Minerals

In natural bodies of water, minerals and trace elements are constantly being replenished through the natural water cycle. But this isn’t the case with your aquarium. On the contrary, your filtration system can actually remove the elements that are needed for a healthy environment. By regularly changing your aquarium’s water, you can ensure that your fish or other aquatic pets have the pure ecosystem they need to thrive.

If you’re going to minimize these dangers to your fish, you need to make changing your aquarium’s water a normal part of your routine maintenance. With that said, the frequency with which you’ll need to change aquarium water will depend on a number of factors, including the size of the tank and the number/type of fish and aquatic creatures living there.

Generally, it’s a good rule of thumb to change between 15 and 20 percent of the water each week. This will ensure that your water stays clear, clean, and livable. If your tank is large compared to the number of fish living there, you may be able to manage with changing it every two to three weeks, but you won’t want to go more than that.

In addition, you should recognize that topping off your aquarium is not the same as changing it. Like any body of water, the water in your fresh or saltwater aquarium will naturally evaporate. Simply adding water will not remove the nitrates or other toxins that could potentially create a dangerous situation for your fish.

How Do I Change My Aquarium Water?

If you follow a regular schedule of changing 15-20% of your tank’s water every week or so, you won’t have to worry about stressing your fish by completely removing them. Instead, you can simply follow these simple steps…

how do I change my aquarium water@svetlanabar / Pixabay
Preparing Your Water

Before scooping a bucketful of water out and pouring a gallon or two in, you need to make sure that the water you’ll be adding is ready. If you fail to do this, you can shock your fish – and even kill them.

So, fill a clean bucket with tap water and treat it with a conditioner. This will balance its pH and minimize any dangerous chemicals that might harm your fish. You’ll also want to ensure that the water you’re replacing matches the temperature and salinity of the water in your tank as closely as possible. Again, adding drastically different water can create a dangerous situation for the life in your aquarium.

If you have a saltwater aquarium, you’ll need to buy saltwater from a local pet store (they often sell them in refillable, 5-gallon jugs) or mix your own using aquarium salt and RODI water. After you’ve prepared your saltwater, make sure to check the salinity so you know whether it matches what’s already in your tank.

Preparing Your Tank

Once you’ve got your new water ready, take a moment to disconnect any lighting or heating elements on your tank to eliminate the possibilities of electrocution or minor shocks. You may also want to check your filtration system at this time, making sure that it’s clean and running properly. Finally, you may want to remove any aquatic decorations or plants that have attracted bacteria or dirt. Give them a good scrub down if they’re looking especially dirty or dingy.

Removing the Old Water

The easiest and best way to remove your tank’s old water is to use a siphon and run it along the bottom of your tank. This will not only pull out old water, it will also remove debris and waste that have settled near the floor of your aquarium. After you’ve removed 15-20% of the old water, check to make sure that the temperature of the tank matches that of the water you’re about to add.

Adding the New Water

Adding your treated water is as simple as slowly pouring it in (always making sure that the temperature and salinity are matched as closely as possible).

Adding the Finishing Touches

Once your tank has been refilled, you can add any newly cleaned decorations or plants and plug all heating and lighting elements back in. It’s that simple.

Can You Change Aquarium Water Too Often?

Generally, you can’t change your aquarium’s water too often. Even daily changes – if done correctly – are completely safe and will ensure that your fish always have a clean environment to live in. With that said, replacing your aquarium’s water that often isn’t really necessary unless you have a difficult time keeping nitrates or other harmful material away.

can you change aquarium water too often@chainfoto24 / Freepik

Why Fish May Die After Changing the Water…

If you’ve ever changed the water in your aquarium and, shortly after, found one of your fish floating, you’ve likely wondered if changing their water could have killed them. Changing aquarium water will not kill your fish – unless the water you’re putting them in is drastically different from what they’re used to.

Like most living things, your fish will adapt to their environment over time. If you replace their current water with water that’s significantly different in temperature, chemical makeup, or salinity, then you could send your fish into shock and even kill them.

So, if you’ve found a dead fish in your tank after changing the water, it wasn’t the mere act of changing the water that led to your fish dying. It was the fact that they couldn’t tolerate the differences in environmental changes.

Don’t be afraid of changing your aquarium’s water. Your fish’s long-term health depends on it. Just be sure that the water you’re adding is as similar as possible to the tank’s current water. By carefully changing your aquarium water, you’ll ensure that your fish and other aquatic pets live as long as possible – and in good health.

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