12 Reasons Aquariums Need Water Changes

There are many reasons aquariums need water changes. Besides keeping up the beautiful appearance of the aquarium, water changes are essential for the health of your fish. Small frequent water changes are one of the best ways that you can maintain your tank. 

So why do aquariums need water changes? Here are some of the reasons to change water in your aquarium:

  • Remove waste and debris
  • Remove accumulated nitrates in the water
  • Remove accumulated nitrites and ammonia
  • Combat evaporation
  • Replace depleted trace minerals
  • Deter algae and cyanobacteria
  • Help maintain the clarity of the water
  • Help an aquarium more accurately mimic natural habitats
  • Maintain pH
  • Re-oxygenate the tank
  • To provide weekly maintenance 
  • Prevent old tank syndrome

Water changes are one aspect of aquarium maintenance that can make a huge difference in the overall health and happiness of your fish. Read on to find out more about the reasons water changes are important and how they affect your tank. 

Water Changes Remove Waste and Debris

On their most superficial level, a big reason to change the water in your tank is to physically remove waste and debris from your tank that cannot be caught by the filter. This includes the following:

  • Uneaten food
  • Dead plant matter
  • Fish poop

Not only is this waste and debris ugly to look at and reduce the overall beauty of your tank, it also has negative effects on the fish. Uneaten food rots, leeching ammonia into the water, as do both fish waste and dead plant matter. 

This kind of debris is not easily caught up by the aquarium’s filtration system, so it often lies on the substrate and degrading the quality of the aquarium’s water. By doing weekly water changes with a gravel vacuum, you can remove most of this waste manually and improve the
water chemistry. 

Water Changes Remove Accumulated Nitrates in the Water

To understand why water changes are important, it’s important to understand how the nitrogen cycle works in an aquarium. 

In the nitrogen cycle, an aquarium with a functioning colony of beneficial bacteria can convert harmful waste chemicals in the water from ammonia, which is then converted to nitrite, which is then converted to nitrate. 

At low levels, nitrates do not have any effect on fish and are a natural part of the aquarium’s water chemistry. However, the higher the level of nitrates becomes, the more toxic the water becomes. Nitrates cannot be removed from the water by filtration and must be removed by changing the water. 

Nitrate poisoning can cause the following symptoms in aquarium fish:

  • Lethargy and listlessness
  • Disorientation
  • Loss of appetite
  • Rapid respiration/gill movement
  • Death

Nitrate poisoning can catch inexperienced fish keepers by surprise because the fish will appear to be just fine right up until the point that the nitrates reach a dangerous threshold. At this point, the fish will deteriorate quickly and may die within twenty-four hours. 

Water Changes Remove Accumulated Nitrites and Ammonia

Along with removing accumulated nitrates in the water, frequent water changes also help keep down the amount of ammonia and nitrites in the water. These chemicals are the by-products of fish waste. 

In the natural environment, these chemicals would be diluted and reabsorbed into the river/lake/sea/body of water. But in an aquarium, these toxic chemicals have nowhere to go, and they are poisonous to fish at very low levels. 

Without a functioning nitrogen cycle, the accumulation of ammonia in a tank will kill fish within hours or days. 

This is why many novice fish keepers set up a tank without a nitrogen cycle, stock it full of fish, and are dismayed when those fish start dropping like flies within twenty-four hours. This is the result of ammonia poisoning. Here are some of the symptoms of ammonia poisoning:

  • Reddened or bleeding gills
  • Fish gasping at the surface of the water
  • Laying on the bottom of the tank
  • Loss of appetite/lethargy

Because ammonia can kill fish very quickly and can cause them prolonged health problems even if
you manage to catch it in time, water changes are vital to keeping the amount of ammonia in the tank water down.

This is especially important when a tank is new and does not have a really strong, established beneficial bacteria colony yet. If you set up a tank with no nitrogen cycle and keep fish in it, you will need to perform daily water changes to prevent the build-up of ammonia in the water. 

These water changes can also disrupt the establishment of beneficial bacteria, which is why it is often advised to not add fish to a tank until after the nitrogen cycle is established. 

This can take several weeks, which means impatient fish keepers often end up killing fish by rushing
the process. 

Water Changes Combat Evaporation

As an aquarium runs, water will naturally evaporate out of the aquarium and lower the water levels
in the tank. If evaporation is allowed to go on too long, it can leave your aquarium heater and pump intake dry. 

This can burn up your filter pump motor (not a cheap piece of equipment to replace) as well as keep the filter from working correctly. Leaving your heater above the water level can cause it to overheat and malfunction, which can either cook your fish or leave them without heat at all. 

Also, as water evaporates from an aquarium, this causes the impurities and toxic chemicals in it to become more concentrated, increasing the amount of ammonia and other toxins per gallon. The higher this concentration of toxins is, the more likely it is to hurt or kill your fish. 

When you do water changes and add fresh, clean water to your tank, this dilutes those impurities and brings the concentration of toxins down, making the water safer and healthier for your fish. Keeping the tank water at appropriate levels also reduces the chance of damage to your equipment. 

Water Changes Replace Depleted Trace Minerals in the Water

Water changes are also important for replacing depleted trace minerals in the aquarium water. These trace minerals have several important functions:

  • Calcium
  • Magnesium
  • Iron
  • Potassium
  • Copper
  • Zinc

These nutrients are vital for the growth of fish and are used up by fish gradually just through the course of them living in the aquarium, so in a closed system, these minerals must be replaced.
Without trace minerals in the water, fish can have nutritional deficiencies that aren’t obvious until the fish are very sick. 

Water Changes Deter Algae and Cyanobacteria

When a fish keeper skips water changes and allows waste to build up in the water of the tank, this creates the perfect environment for the colonization of algae and cyanobacteria.

Not only are these lifeforms unsightly and greatly reduce the cosmetic quality of the tank, once they get started it is very difficult to rid the tank of them without drastic measures like doing a deep clean of the entire tank (which is very stressful on the fish) or keeping the tank in total darkness for days or weeks. 

Cyanobacteria, or blue-green algae, is not actually an algae but rather a type of photosynthetic bacteria. One of the major dangers of cyanobacteria is that it can drastically drop oxygen levels in the water, enough that the fish do not have enough oxygen to live. 

Water changes prevent the stagnation that allows algae and cyanobacteria to establish themselves, and it is much better for the tank’s overall health to prevent these problems rather than have to beat them back once they’re begun. 

Water Changes Maintain Clarity of the Water

On a more cosmetic level, frequent small water changes are one of the best ways to maintain the clarity of your aquarium’s water. Old aquarium water full of impurities becomes yellowed and ugly to look at, especially under bright LED aquarium lights. 

Once you do a water change, you will see that the water in the tank is sparkling clear, and it is much easier to see and enjoy your fish and aquatic plants. Since water changes also deter the growth of algae, this will also keep the sides of the tank easy to see through. 

Since there is little point in having an aquarium if you can’t easily see into it, water changes are the best way to maintain the appearance of your tank. 

Besides the cosmetic benefits, changing the water reduces the number of particulates in the water (these are the microscopic debris that cause water to look yellowed or cloudy), and these particulates make it more difficult for fish to breathe easily. 

Water Changes Mimic Natural Environments

When fish live in the wild, they do not typically live in a static, stagnant body of water (with very few exceptions not often found in the aquarium world). Most common aquarium fish are from rivers, streams, lakes, and oceans, which are dynamic, changing bodies of water. 

These bodies of water are subject to water changes in the form of currents that push waste water further downstream and rain that helps to further dilute them. They are also large, and fish can remove themselves from sources of bad water by simply migrating elsewhere. 

An aquarium keeper also has to think about this in terms of gallonage. A river has thousands upon thousands of gallons of water in it, so biological toxins are very diluted and constantly swept away. Compare that to a ten or twenty-gallon aquarium, where toxins are allowed to accumulate, and fish have no way to swim away from them and into cleaner waters. 

Water changes not only mimic natural environments and make the fish objectively happier, they also mimic natural water cycles, which constantly refresh water sources with fresh, clean water. As a responsible fish owner, people with aquariums are obligated to provide similar refreshment. 

Water Changes Maintain pH

Trace minerals in the water are important for another reason other than the nutrition of the fish. 

These minerals act as buffers in the water to help maintain pH stability, and pH is a water parameter that many fish are sensitive to. Without those buffers, the water suffers from large swings in pH, and that alone is enough to stress and kill many kinds of aquarium fish. 

Some fish are more susceptible or vulnerable to pH swings than others, but all are considerably stressed by them. So for the best interest of the fish, it is important to change water frequently and prevent pH stress. 

If fish suffer a large swing in pH, they can succumb to the following symptoms of pH shock:

  • Panicked thrashing/darting around the tank
  • Gasping
  • Trying to jump out of the tank
  • Later line erosion
  • Poor coloring

Some symptoms of pH shock (such as thrashing) are the result of a large pH swing, usually caused by too large of a water change without pH buffers. Other symptoms, such as lateral line erosion, are caused by gradual pH problems and are the result of infrequent water changes. 

Water Changes Re-Oxygenate the Tank

When a fish keeper sets up a bucket or jug of fresh water for an aquarium, this often comes from a faucet or hose that pushes a bunch of dissolved oxygen into the water.

Fish receive dissolved oxygen from the turnover of the filtration system (if it has a waterfall) and from aeration equipment like air stones or curtains, but if an aquarium has a lot of algae or a large stock of fish, oxygen levels can still run dangerously low. 

Doing frequent water changes adds a large dose of oxygen to the tank all at once, which greatly increases the quality of life for the fish. A person can see the positive response that fish have to a water change in their increased activity and liveliness directly following a water change. 

This is because the water is freshly oxygenated, which lets all the fish breathe that much easier. Without a steady flow of oxygen, fish will gradually suffocate and die. For this reason, water changes are even more important in tanks that do not have a filtration system. 

Water Changes Allow for Weekly Maintenance

If you schedule a small partial water change once a week, this task allows a fish keeper to perform many other operations of maintenance on the tank at the same time, such as the following tasks:

  • Monitor water chemistry: Just prior to a weekly water change is the best time to do a water chemistry test and see where the water parameters are. This allows for a fish keeper to adjust the parameters by adding chemicals during their water change.
  • Clean the substrate: Most of the debris, such as uneaten food and rotting plant material and fish waste lays on the bottom of the tank and is not taken up by the filtration system. By performing a water change, you can use a gravel vacuum to siphon this waste away.
  • Fertilize aquatic plants: A water change is a good time to add liquid fertilizers to your tank if you have live aquatic plants. While these fertilizers only have to be added once every couple of weeks, adding them during a regular water change twice a month can have very positive effects on the health and quality of your plants. 

Water Changes Prevent “Old Tank Syndrome”

While many fish keepers hear about new tank syndrome, which is when an aquarium is set up without a functioning nitrogen cycle, and fish begin to rapidly die off, old tank syndrome is a less talked-about problem with aquarium keeping.

Fish keepers can become complacent, and this can lead them to change water less and less frequently the longer they have a tank. The symptoms of old tank syndrome are as follows:

  • Build-up of algae 
  • Increased phosphates and nitrates
  • Falling pH (acidic water)

In an attempt to combat old tank syndrome, many fish keepers decide to do a massive deep cleaning of the tank. This is possibly one of the worst things you can do in this situation because it subjects the fish to even more rapidly changing water conditions. 

If a large water change is performed to combat old tank syndrome, it is not uncommon for many of the fish to suddenly die. 

Instead, if your tank is suffering from old tank syndrome, the answer to the problem is frequent water changes. To correct bad water chemistry as quickly as possible, water changes of ten to fifteen percent should be performed on a daily basis until the chemistry is corrected. 

This small water change will not be enough to hurt or disturb the fish, but it will help the fish keeper gradually get control of the water parameters. If pH changes or parameters start to shift in your weekly or bi-weekly water chemistry tests, it might be time to step up your cleaning and water change schedule. 

Water Changes Keep Your Fish Healthy and Happy

There are many reasons you should perform water changes, but the most important reason is that a consistent water change schedule is the driving force behind a healthy aquarium.

Not only do frequent water changes encourage you to keep a close eye on the parameters of your tank so you can catch problems early, but it also helps to prevent many of those problems from becoming an issue to begin with.