The Importance of Water Changes in Aquariums

March 17, 2021 Phil Overton

Water is the basis for life, which is why the quality of the water hosting life is undeniably important. This is especially true when it comes to your aquarium. Because aquariums are closed systems, nutrients, contaminates, and chemicals can easily accumulate, in which, with time, will cause an unbalanced ecosystem and poor water quality. Water quality is not just an aesthetic concern but crucial for the continuous health and growth of your aquarium inhabitants. Regular tank maintenance is critical in maintaining your aquarium’s water quality. One key element of routine maintenance is water changes.

Symphysodon discus in an aquarium on a green background

The Benefits of Water Changes

Lowers Nitrates  

The Nitrogen Cycle is a natural occurring process where beneficial bacteria will break down harmful ammonia and nitrites converting them into less harmful Nitrates and under some conditions, into nitrogen gas.

Although nitrates are less harmful to your aquarium inhabitants than ammonia or nitrites, they can become a threat if the levels become too high. High nitrate levels are usually associated with algae growth in a tank because nitrates are a fertilizer for plant matter. Although algae can be beneficial as a natural food source, it can get out of control quickly and take over your aquarium. Excessive algae growth is unappealing and, in the worst cases, can jeopardize your aquarium’s inhabitants by depriving the tank of oxygen. If the oxygen level in the water drops below 4 ppm, you will see obvious signs of stress on your fish, and if it continues to drop below 2 ppm, death will follow soon after.   

Almost all aquatic life will experience detrimental injuries when exposed to high levels of nitrates. It can cause your fish to be vulnerable to diseases, experience kidney damage and decreased fertility, have poor growth, and will reduce their lifespan. In reef tanks, elevated nitrate levels may even cause a spur in the growth of zooxanthellae, which, in turn, competes with the coral host for inorganic carbon, causing a decrease in the growth of the coral. Hobbyists may notice this happening as a darkening/browning to the coral.

If you do not have your system set up to fully complete the Nitrogen Cycle (where nitrates are converted into nitrogen gas), then the nitrate level will accumulate over time and will eventually become too toxic for your aquarium inhabitants. This is because the aquarium is a closed ecosystem which does not allow nitrates to be eliminated or diluted on their own. This is when your best option is to physically remove nitrates by performing regular water changes.

For more information on the Nitrogen Cycle please see our blog:

And check out MarinePure® products, which can naturally remove Nitrates.

Improves water clarity

The truth is, all hobbyists, no matter how experience they are, have struggled with cloudy water. That is because there is not a one single, simple reason for why the water is cloudy. However, observing the color of the water and the circumstance on which it appeared can help you find the cause and the solution.

Common reasons for a cloudy aquarium are:

Unwashed Substrate – If your water is cloudy within two hours of filling up your tank, it is most likely due to an insufficiently washed substrate. Substrate like gravel and sand contains really tiny particles, which would cause your water to get cloudy if the substrate was not rinsed thoroughly. 

Overgrown algae aquarium on a white background

Bacterial Blossom – As your new aquarium goes through its initial cycle, it is very common for your aquarium to become a little hazy/cloudy. One bacterium is invisible, however as it starts colonizing, the group will cause a foggy discoloration in your aquarium’s water. It takes several weeks and even months to establish bacterial colonies that will perform the biological removal of wastes. However, if your aquarium has already completed the cycle process, then bacteria bloom may be a sign of decaying plants/fish, a faulty filter or too much waste build up. If your aquarium is struggling with waste buildup it may be that you are overfeeding your fish, or your aquarium may be overstocked. If this is your case, then having the correct biological filter along with a good mechanical filter may be of great use to you.

For more information on mechanical and biological filtration and how MarinePure can help please check out our blog:

Algae growth – If you noticed your aquarium water is turning green, it is due to algae growth. There are several reasons why you are having an algae outbreak. You may be exposing your aquarium to too much light. Or your aquarium is having an issue with excess nutrients such as high phosphates and nitrates. Phosphates come from decaying fish food or from your water source. Testing your tap water for phosphates will let you know if you have a problem with your water source. Nitrates are a byproduct of fish waste and can be detrimental to your aquarium inhabitants if left to rise to high levels. Setting up your aquarium’s biological system to fully complete the Nitrogen Cycle is very beneficial, especially if you are struggling with high Nitrate levels. The only way to naturally convert Nitrates into Nitrogen Gas is to create a low oxygen zone/region in your system. However, not all bio-filter media will successfully complete the Nitrogen Cycle. We encourage all hobbyists to do ample research.

Dirty glass of aquarium. Algae growing on the surface of fish tank. Abstract view of green slimy organism background

Removes odors

All aquariums emit a slight smell. Freshwater aquariums have an earthy scent, while saltwater aquariums have an ocean scent. These aromas are perfectly normal for your aquarium. However, if your aquarium starts emitting nasty odors then it is time to find the cause and take action. 

Common reasons for a smelly aquarium are:

Overfeeding, Fish waste & Substrate – It is common for some particles to fall quickly to the bottom of your aquarium rather than float to the mechanical filter. Which is why it is completely normal to find waste trapped in the substrate. Your fish will only eat a certain amount of food and whatever they do not eat will simply fall to the bottom of the tank. The same goes for fish waste. Waste that is not removed and stuck in the substrate for a long time will decompose and produce an odor.

Rotting Plants/Fish – Some fish like to take refuge behind decorations which may make it a little hard to spot a dead fish. Rotting plants are easier to spot because they will turn black or brown. It is important to immediately remove the rotting plants/fish to prevent additional problems like rising ammonia levels. Ammonia is highly toxic for aquarium inhabitants, and even in low concentrations it can severely stress the fish and cause the fish to lose its appetite.   

Dirty Filter – It is the mechanical filter’s job to keep the water clean. It will filter the water to trap particles like fish waste, food, algae, and dust. This is exactly what you want your filter to do, remove the floating particles out of the water making sure the water stays clear and clean. However, these particles will break down and if the filter is not being cleaned regularly, the filter will start emitting odors. 

Routine water changes help to remove odors and discoloration from the aquarium water. This is not only an aesthetic benefit, but it is especially beneficial for reef and planted aquariums. For proper growth of photosynthetic corals and invertebrates, you need to have the right light intensity. However, making sure your corals and invertebrates are receiving the right amount of light is difficult to achieve with turbid water. Routine water changes will help you maintain clear, clean water for optimal light and healthy living organisms.

Helps remove decomposing waste particles

Have you ever stirred your substrate and find yourself surprised to see how much detritus is present? Mechanical filtration will remove any solid waste, dirt and particles that are floating through the water. However, some will still accumulate at the bottom of the aquarium. Over time, these particles decompose and release nitrogenous byproducts, phosphates and other chemicals which leads to poor water quality. In severe cases, the decomposing organics creates an acidic environment which can hinder the pH balance of your aquarium. A compromise to the pH can be detrimental for all aquariums. Routine water changes creates a routine removal of these particles.

You can maximize your results by using a siphon that “vacuums” the gravel while extracting the water, pulling out particles that have settled at the bottom of your aquarium. However, you must keep in mind that vacuuming your gravel may remove beneficial bacterial if the tank’s gravel was the only source of biological filtration in the system. This can lead to an interruption to the ecological balance of the bed, which can then lead to spikes in ammonia and nitrites. Having a properly set up biological filter solves this problem.

Replenishes depleted minerals and trace elements

In marine aquariums, vital minerals and elements are usually removed through filtration or depleted as corals and invertebrates use them to grow. Trace elements like iodine, iron and strontium are vital for corals and aquarium organisms to grow well and remain heathy. Fish need trace elements in their diet to have a healthy and fully functioning immune system. Even aquatic plants will use trace elements for nutrition and as fertilizers. Iron is used by aquatic animals for oxygen transport, and corals will use it for photosynthetic activity. Strontium acts a lot like calcium, in the sense that stony corals will use it and incorporate it into their aragonite skeletons. Manganese is another trace element that has shown to help with corals’ abilities to resist stress and bleaching. Trace elements are found in fish food; however, water changes provide you the opportunity to add conditioned water that will supply more of the necessary supplements for proper growth. It is also a time to adjust a saltwater tank salinity that may have become more concentrated due to evaporation.

May aid in resolving unexpected problems

Whether or not you are new to the hobby, unexpected changes/problems in your aquarium will happen. Finding the cause of the problem and resolving it before it gets worse is the key for a long-term successful aquarium. Ultimately, an issue with the water quality is the reason for most aquarium problems. Water changes may aid and even be necessary for some unexpected problems, such as cloudy water, diseases, sluggish and/or dead fish. Having the right biological filter for your aquarium will also aid you by providing more surface area than necessary. Therefore, in the case where there is an upset to the aquarium, the bio film and bacteria will have enough space to expand and do their job of removing harmful byproducts without competing for space and without the media getting clogged by its own biofilm growth.

For more information on common biofiltration issues, please see our blog:

How often should a water change be done?

The general recommendation is 10% of the tank’s water volume weekly, or 15-20% every other week, or 25% monthly.

However, the answer to this question depends on several factors:

  • The size of your aquarium
  • The type of fish and living organisms
  • The quantity of living organisms
  • The quality and efficiency of the biological  and mechanical filters   

Many aquarists have found that with a proper filtration system with well-established beneficial bacteria can greatly reduce the amount of water change needed, as well as the frequency of the water changes, saving time and money.

Cutting tongs old aquarium plant

Additionally, you may like to implement other tasks at the time of water changes. For example, inspecting the filter and media, wiping down inside glass, siphon substrate, water testing, trimming live plants, etc. Is never wise, to clean everything all at once, therefore establishing a routine that works for you and your aquarium is extremely important to keep your aquarium clean and its inhabitants healthy. Ultimately, some trial and error are required to determine the most effective water change routine for your specific aquarium.

How can MarinePure® help?

MarinePure is a man-made ceramic biofilter media that combines a large amount of usable surface area with open/interconnected pores. This combination allows MarinePure to be the perfect media to use if you would like to make sure your aquarium is optimized to start and complete the Nitrogen Cycle efficiently. Because of MarinePure’ s unique composition, water easily flows all round and through the inner structure of the media. This allows for nitrifying bacteria to colonize on the outer layers of the media where Oxygen is present and denitrifying bacteria to colonize in the inner structure of the media where it is practically Oxygen free. If you would like to have even more control of your nitrates, place the media in a passive/low flow area in your sump. Doing so, increases the low-oxygen area allowing for more anaerobic bacteria to grow.


Due to MarinePure’ s high surface area, it ultimately provides your aquarium with extra capacity for bacteria growth. This is essential in the case your aquarium ever has an upset, such as diseases or decaying fish, or if you simply would like to house more fish in your tank.

MarinePure also reduces the need for water changes due to the lower nitrate levels you will be able to achieve and reduces maintenance because it contributes to a more consistent water chemistry and it does not need to be cleaned regularly. If you would like more information on MarinePure biofilter media please feel free to reach us out at   

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