How Often to Change Water in Your Aquarium?

Water changes are an essential part of regular aquarium maintenance. Your aquatic pets are continually producing waste, while uneaten food and other organic elements accumulate in your tank.

There is also the waste that you cannot see, like ammonia and nitrates. The frequency with which you change your aquarium will depend on the kind of setup you have.

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Smaller tanks, for example, require more changes while waste is diluted more effectively in larger structures. Some fish also produce more waste than other varieties.

You can use the guideline below to create an aquarium maintenance schedule:

Water Changes in the Nitrogen Cycle Period

You will need to cycle a new tank before adding any aquatic pets. In the wild, fish live in a well-balanced ecosystem that includes a nitrogen cycle for recycling nutrients and waste.

You will need to trigger this cycle in your set up to allow beneficial bacteria to accumulate in your biological filter.

The nitrogen cycle, also called the New Tank Syndrome or Nitrification process, makes the aquarium environment safe for your fish by neutralizing their waste. It takes about 6 to 8 weeks and you have to ensure that the process is finished.

The cycle begins with the introduction of ammonia into your tank via fish waste. This element will keep accumulating until the bacteria that break it down starts to form. You may notice your tank becoming cloudy once the bacteria begin working.

The Nitrosomonas bacteria will oxidize ammonia into nitrites, which is still toxic to fish. The levels of nitrites will continue to increase until the appropriate bacteria forms to break it down.

The Nitrobacter bacteria are responsible for turning nitrites into nitrates. Nitrates are not harmful at low levels but they will become hazardous past 20ppm.

Your tank will be fully cycled once the levels of ammonia and nitrates are at 0ppm.

Some beginner aquarists refrain from doing water changes during the cycling process to avoid disturbing the forming bacteria. The beneficial bacteria have, however, been shown to be great at holding on to filtration surfaces.

Performing regular changes in a cycling tank does not interrupt the cycling process. High levels of ammonia and nitrites also reduce the amount of oxygen in your tank.

The beneficial bacteria you are trying to cultivate require oxygen to develop, as do the fish that are added in the cycling process.

Aim to change at least 30-50% of the water twice a week in a cycling aquarium.

Regular Water Changes

It is recommended to change 10-30% of your tank water every week, once your aquarium is established.

You will need to pretreat the replacement water to ensure it is safe for your fish. If you are utilizing tap water, let it sit overnight so that the chlorine can evaporate.

You can also use a water conditioner rated for aquarium use. The water should be given time to attain room temperature.

It is advisable to unplug the lighting, heating, and filtration elements. Most filters do not function correctly without full water coverage, while exposed heaters can break, crack, or overheat.

While you do not need to clean your tank’s ornaments with every water change, you may need to remove any accessories that look slimy. Soak such decorations in a plant-safe cleaning solution.

Evaluate the walls of your tank as well to determine if they require a scrub. You do not want to miss any brown or green film.

Move your siphon around to suck out a maximum of 30% of your tank’s water. Any more and you risk affecting the balance of your aquarium. You can also rinse your tank’s filter media if it appears excessively dirty.

Importance of Water Changes in the Aquarium

Although your aquarium is equipped with a modern filtration system, you still need to perform water changes. Filtration media slows down the accumulation of harmful elements, but it is not capable of solely maintaining the water quality.

A significant benefit of water changes is the removal of ammonia, nitrates, and nitrites. If these elements are allowed to collect in a fish tank, your fish will become stressed and susceptible to diseases.

Decomposing organic materials also pose another challenge to water quality in an aquarium. Organic waste will release nitrogenous chemicals, phosphates, and other toxic elements to the aquatic environment.

The replacement water also introduces essential minerals and trace elements like iron that are abundant in the wild habitats of your fish. Such minerals support various functions in the body of a fish.

Water changes also improve water clarity by removing discolorations and odors. Clear water is able to absorb maximum light to support the growth of live plants.

Can You Skip a Water Change?

You can skip water changes occasionally, provided your water is free of toxic chemicals like nitrates and ammonia. It is, however, best to stick to a regular water change schedule.

Can You Replace All Aquarium Water at Once?

It may be tempting to perform a 100% water change when faced with an algae outbreak, deteriorating water conditions, or other extreme circumstances.

If you change all the water in your aquarium, however, you will drastically reduce the level of nitrifying bacteria and disrupt the processes of breaking down organic matter.

The quantities of nitrites and ammonia will thereby increase and create a toxic environment for your pets. You can end up with more severe problems like a worse algae bloom.

Frequent water changes are recommended because they do not affect the chemical balance in the aquarium.

How to Increase the Time Frame Between Water Changes?

If you want to reduce the frequency of water changes, you can populate your tank with fast-growing aquatic plants. The plants will eliminate harmful elements like nitrates from the tank water.

Automatic Aquarium Water Changes

Performing water changes can be a tasking affair, which is why automatic water changers are incredibly helpful.

Automatic water changers suit aquarists or aquarium shops who have multiple or huge aquariums. Usually, for multiple aquariums, you will need to setup a complex plumbing system, which will supply fresh water to each aquarium. Also, you will need to extract the old water from the aquarium.

Setting up an automatic aquarium water change system is not easy, so may not be feasible for people with a single tank.

Depending on the size of your aquarium, you can still consider a small automatic water change system – I recommend this device by AutoAqua on Amazon.


In the wild, fish exist in a naturally balanced ecosystem with a lot of key players. An aquarium is a closed system which means that you have to introduce beneficial bacteria and remove unwanted elements.

Before adding your aquatic pets to your set up, ensure that your tank is well-cycled by triggering the nitrogen cycle.

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