Fish Tank Water Parameters That Can Kill Your Fish

How can ammonia, nitrite, nitrate, pH, and temperature impact the Fish's well-being? How to effectively maintain a safe environment for your Fish Tank?

When keeping fish in an aquarium, it is critical to keep the water health consistent so that the fish are able to maintain their health. 

What are some fish tank water parameters that can kill your fish? Harmful ammonia and nitrates can build in the tank and kill your fish. Proper water temperature and pH can ensure your fish are in their optimal environment. Treating your water to remove harmful substances is also critical for fish health, but treatment should only be done when the fish are not in the water. 

Since fish are not meant to be in small human-controlled aquariums, it is critical to be aware that the water in an aquarium will not self-regulate the way water in the ocean or a free-flowing source of water would. In this article, we will cover how to regulate your water system to ensure optimal health for the fish that are living in your aquarium. 

Freshwater Fish Tank Water Health

Why is Water Health Important?

Water that is inhabited by any aquatic animal gets filled with waste products over time. Whether it’s decaying matter or just simply waste from fish. These products need a way to be filtered out of the water so that fish are not continuously taking in their own waste products. Generally, the habitats fish live in would be effective in filtering on their own.

Fish that are living in the wild in a stream, lake, ocean, wherever they may be, are in an ecosystem that is able to go through its own life cycle to keep all the animals living there healthy. Regardless of the species of fish, it needs to be in an environment that is able to filter through the water or they will get sick and likely die from unhealthy water. 

If water is not properly filtered it is likely there will be a buildup of ammonia and nitrites from waste materials being secreted into the water. Most often, these are absorbed or filtered by bacteria and plant life that is naturally occurring in the water. However, in an aquarium tank setting these filtration systems need to be thought through and implemented. 

In wild settings, the larger the body of water, the less lethal any buildup of chemicals or waste materials will be to animals. This is going to remain true even in an aquarium setting. The larger the tank, the easier it will be to maintain balanced water levels and keep your fish healthy. In smaller tanks, you will need to be much more vigilant about checking the water health. 

How to Tell if Your Fish in Tank is Sick

If you have not been diligent about keeping your water levels healthy or are unsure if your fish is sick or not, there are some critical signs to look for to determine if your fish is healthy. The first is the way your fish is swimming. Be sure to take note of how your fish generally swims so that you have a baseline to compare to across the lifespan of your fish. 

If you are seeing that your fish is swimming upside down or is moving in a different nature than is typical for the individual, this could be a sign that your fish is not healthy. Disorientation can be a sign of toxic chemical buildup in the water that needs to be filtered and cleaned out to get back to a more balanced state. 

Another sign to look for is if the fish is eating its food. Any healthy animal will also have a healthy appetite. If your fish is leaving all of its food untouched that is likely a bad sign and indicative of the health of the fish. Other behavioral changes can include rubbing on hard surfaces or being socially isolated from other fish if housed with any.

Social isolation is very common in animals before they die as they are basically leaving their family group to go off and die somewhere. If your fish is housed with other fish and is usually in a group and starts showing this behavior, that is a clear warning sign that the fish is sick. 

Another factor to look for is any trouble breathing. If your fish is gasping at the surface of the water this is a sign that they are having trouble breathing. This could be due to unbalanced water that needs treatment or replacement. However, be aware that you will often see physical changes in addition to behavioral changes. 

If you are seeing any white spots on the fins or body of your fish, as well as any discolored gills, this could be telling of something being off in the water that your fish is living in. Whether it be an overgrowth of bacteria or yeast that is attached to your fish or some kind of toxicity, this is a clear sign that your fish’s health is being impacted. 

Other physical changes that may be noticeable when your fish is sick include any bulging of the eyes, this can happen in one eye or in both. Any accumulation of mucus on or around the body of your fish. Any skin lesions or sores, this is often a result of them rubbing on hard surfaces as mentioned above, and can be extremely harmful to them.

Bloating of the body is another sign that the fish is in poor health. And finally, if you see any physical changes in the shape or size of your fish, this is often a bad sign. For example, a crooked back is often observed in sick fish. This can be telling of an unhealthy individual.

Common Causes of Illness Fish Tank Fish

If you observe any of these signs or symptoms in your fish, be aware that there is a plethora of reasons as to why they may be occurring. This could have to do with their water, but also may not. It is important to consider all options as otherwise, you may not know how to properly care for your pet. 

First, if your pet has a physical injury some of these symptoms may be a common response. Most often you will be able to observe a physical injury and move forward with caring for your fish. If you do not see any signs of physical injury, it is likely something else that is causing issues for your fish. 

Any white spots that you see on your fish can be parasites, this is often caused by unclean water that has too much waste. If there is a lot of waste in water, that leaves a higher potential for parasite infestation. Common parasites include nematodes, anchor worms, fish lice, gill maggots, and monogenean flukes. 

If you believe your fish has parasites, the first step is to thoroughly and deeply clean the tank out and replace the water. After scrubbing down your tank, rebalance the fresh water inside and ensure everything being put back in the tank is disinfected so that you are killing off any parasites that may be in the tank. 

Other infections can include bacterial and fungal infections. Any infection caused by a bacteria or fungus can lead to diseases like fin rot or ulcer disease which cause the rotting of a fish’s fins. There are a number of diseases fish can contract but remember that often this is not due to their water and may be unavoidable. 

With that in mind, it is never a bad idea to clean the tank and change out the water. This will have no negative effects on your fish and will only increase their health. As oftentimes, the symptoms stated above can be caused by ammonia or chlorine poisoning which is a direct result of poor water quality in the tank. 

Ammonia is going to be the direct result of not changing the water out frequently enough as ammonia accumulates due to the buildup of waste in the system. Whereas chlorine often builds in the system when the water is not balanced when replaced or is not balanced frequently enough. 

These are problems that are extremely easy to avoid and will prolong your fish’s lifespan. Changing out the water and remembering to balance it when you do will only take you a little bit of time in your day and should be prioritized at least once a week, if not more often depending on the size of the tank. 

The frequency of water changes also depends on how many fish you have in your tank. The more fish you have, the more frequently you should consider changing the water. You should never go longer than about two to four weeks between changes, depending on tank size and occupancy. 

The longer you go between water changes, the more likely you are to wind up with dead fish or sick fish who are exhibiting some of the symptoms mentioned above. 


Balanced Water Elements are Key to a Healthy Fish Tank

How to Balance Water in Fish Tank

Now that we’ve talked about how to identify if your fish is sick and what some potential causes could be, let’s talk about how to balance the water in your tank to ensure that you are not putting your fish’s health at risk. Among the most important aquarium parameters to maintain in your tank include:

  • Ammonia levels
  • Nitrite levels
  • Nitrate levels
  • pH
  • Phosphate levels
  • Silicate levels
  • Chlorine levels
  • Water hardness
  • Waste

Ammonia Levels

A buildup of nitrogen compounds is generally due to the breakdown of aquarium waste. The breakdown of nitrifying bacteria causes levels of ammonia in the tank to skyrocket to unhealthy and dangerous levels. There are two chemicals, ammonia, and ammonium, that can both be picked up by a total ammonia test kit. 

If you have balanced your water and your test kit is still detecting ammonia, you need to take immediate action to correct the balance of the water or else your fish will most likely die within a few days. You can use products such as Algone Water Clarifier and Nitrate Remover to clear and prevent cloudy water buildup in the tank and remove nitrites and ammonia buildup.

Even if you detect a low concentration of ammonia in your tank, this can cause huge stress to your fish and result in serious health issues. A buildup of ammonia makes your fish more vulnerable to contracting diseases which in turn results in a shortened lifespan. Therefore, if you leave your fish in this environment for too long it will surely die.

While ammonia buildup is highly toxic and lethal in freshwater aquariums it is even more detrimental to fish in reef or saltwater environments. Due to a higher pH in saltwater aquariums, the buildup of highly soluble ammonia gas is significantly more toxic to the fish living in the aquarium. 

Therefore, depending on the nature of your aquarium tank, it may be even more important to keep up with your ammonia levels. However, keep in mind that regardless of if your water is fresh or salt, you need to check your ammonia levels consistently or else you will continue seeing your fish dying off.

Nitrite Levels

Nitrite is enabled to build inside your aquarium as soon as ammonia is available inside the tank. This is the second stage of the nitrogen cycle and the nitrite bacteria multiplies and colonizes quickly inside your tank. The bacteria Nitrosomonas is the primary way that ammonia is converted to nitrite inside fish tanks. 

This cycle continues once nitrite is present, and the bacteria Nitrobacter converts the nitrite then into nitrate. Be prepared for your nitrogenous compound levels to be high after you set up a new aquarium is initially set up. This is necessary for the bacteria to form a colony in the tank. 

This initial process is toxic but is then a waste conversion system that will perform the nitrogen cycle within your tank. These aerobic bacteria forms in the tank as a way to accomplish the nitrogen cycle and require a constant flow of oxygen to perform that task. However, keep in mind that nitrite should not be detectable once the nitrogen cycle is established. 

While it is establishing it may be a good idea to keep your fish elsewhere. Once the cycle is established, when you test your water it should not be detectable. If it is, your water levels are off. Nitrite is not as toxic as ammonia but will cause stress to fish at levels as low as 0.5 ppm. Keep that number in mind when testing your water.

If your nitrite levels continue to be more than 10 ppm to 20 ppm it will end up being lethal to the fish. If these levels are consistent or even detectable for more than seven days, you should take immediate action to balance the water before your fish die from the excessive levels of nitrite in the tank. 

Nitrite directly interferes with the way fish are able to metabolize oxygen, therefore if your nitrite levels are exceedingly high it will, in turn, destroy the fish’s hemoglobin in their bodies which is the cell that carries oxygen. 

Nitrate Levels

The third and final stage of the nitrogen cycle is the development of nitrate in the fish tank. The process takes waste and turns it from ammonia to nitrite to nitrate. Unlike the first two chemicals, nitrate is commonly detectable inside an aquarium even after it’s established. This will not negatively impact your fish or their health.

The main function of nitrate is in causing the growth of algae in the aquarium and can cause green water to form in the aquarium. If you keep your nitrate to a minimum you will avoid any excessive algae growth in the tank which can lead to ugly and messy outbreaks. This can be difficult to clean and create excessively cloudy water. 

Although nitrate is not as toxic to fish as ammonia and nitrite, it is still a nitrogen-based compound that will still cause stress on your fish’s organs. This makes it harder for the fish’s body to function at normal levels within its environment which can also lead to a shorter lifespan due to organs functioning in overdrive. 

With the increased stress on the fish’s body, it will be less able to fight off diseases and have a decreased ability to heal itself and reproduce. Therefore, even though nitrate is not going to pose as big of a threat to your fish as nitrite and ammonia will, it is recommended to still keep it at a minimum since it can cause increased stress. 

To lower or dilute levels of nitrate in your aquarium it may not always be enough to change the water in the system as it can often stick around in the tank even if you do change the water. If you see a rising level of nitrate, using Algone in between water changes will reduce the levels of nitrate in your aquarium and maintain your water clarity. 


The pH of your water is the power of hydrogen available in your water. This is the measurement of hydrogen ions in your water, with increased hydrogen ions there is less bonding, which drops the pH and creates more acidic water. If there is a decrease in hydrogen ions the pH rises, which creates more alkaline water. 

Sudden and frequent changes in water pH are a very common cause of death in fish, even though they are able to adapt easily to various pH levels, this is limited to an ideal range. For most species, it is ideal to stay in a range between six and eight. However, if your pH is constantly changing, the fish will not be able to adapt well. 

The change in pH is not ten-fold between numbers, therefore if you are changing the pH from seven to six the water is getting 10 times more acidic. That is why any changes to pH can be difficult for fish to adapt to when it is inconsistent. When changing the pH of your aquarium make sure you’re taking carbonate hardness into account. 

The pH of harder water is going to be more challenging to adjust because it continues to bounce back to its normal level. While soft water is more easily adjusted because it stays put after being adjusted. To make pH changes stick, make changes incremental so that your fish can adjust accordingly. 

However, make it your goal to maintain constant pH so that you do not have to consistently adjust the pH. It is also good to keep in mind that ammonia is more toxic to your fish when your water is at a higher pH. Whereas the growth and activity levels of nitrifying bacteria begin to decline to start at a value of pH six and lower. 

Water Hardness (GH)

Water hardness is primarily measured by the calcium and magnesium ion levels in the water. Water GH levels are going to be more important for those who are breeding their fish as there are specific requirements for breeding systems. 

Some species require very soft water for optimal breeding; however, soft water is difficult to maintain and will require consistent adjusting. If you are keeping fish just as pets, you will not need to focus as much of your time on the water’s hardness. 

Carbonate Hardness (KH)

The carbonate hardness is measured by dissolved ions in bicarbonate and carbonate. These ions are primarily responsible for the buffering capacity of the water. This determines how stable the water pH is, the more ions that bond with the hydrogen ions, the fewer carbonate ions bonded which lowers the pH. 

If your water has a KH of 70 ppm or lower, you will see a crash in your pH. If you need to increase your KH levels, baking soda is effective in increasing the pH. However, it is recommended not to adjust the KH levels in your water unless it is absolutely necessary. If you do make an adjustment, be sure to take it slow to avoid stress on your fish. 

An increase of increments of 0.5 pH is safe for your fish but should not be taken any faster than this. Depending on how much you need to adjust, you should take this process over the course of days, rather than trying to get it all done in one day. 

Phosphate Levels

Phosphate is a product of the mineralization of waste minerals in your aquarium tank. This includes waste from plant matter, bacteria buildup, fish excrement, food waste, and the slime created by fish. These waste products can get stuck in your water filter and settle into the water.

To manage phosphate levels be sure to rinse your filter materials and clean your gravel during every routine cleaning. This will reduce the accumulation of phosphate in your tank and remove the sources that are producing high levels of phosphate. 

Chlorine and Chloramine Levels

The water companies that supply our water utilize chlorine and chloramine to disinfect tap water from other bacteria and contaminants. However, both of these chemicals are harmful for fish and need to be neutralized before putting fish into the water. 

Chlorine can be aired out, however, chloramine does not and consists of a mixture of ammonia and chlorine. This substance passes through the fish’s tissue directly and can infiltrate the bloodstream. Once in the blood, it will destroy the ability of the fish’s cells to carry oxygen which can kill your fish within 24 hours. 

This can be avoided by using a quality water conditioner to ensure the water is safe and suitable for fish.


The temperature of the water in the tank should be appropriate for the specific species of fish. Too high or too low of a temperature can be stressful for fish and can lead to illness or death.

It is important to keep it within a range that is appropriate for the specific species of fish you are keeping. Different species of fish have different temperature requirements, so it is important to do your research and make sure you are providing the right conditions for your fish.

In general, most tropical fish prefer water temperatures in the range of 76-82 degrees Fahrenheit (24-28 degrees Celsius). However, some species may have different temperature requirements, so it’s important to check the specific needs of the fish you are keeping.

It’s also important to make sure that the temperature of the water in your tank is stable and does not fluctuate too much. Sudden temperature changes can be stressful for fish and can lead to illness or death.

If you are unsure of the appropriate temperature range for the fish in your tank, it is a good idea to consult a veterinarian or a knowledgeable fish store employee. They can help you determine the best temperature range for your specific species of fish.

Here are a few examples of temperature requirements for some common freshwater fish:

  • Goldfish: Goldfish are coldwater fish and can tolerate a wide range of temperatures, from about 60-70 degrees Fahrenheit (15-21 degrees Celsius).
  • Angelfish: Angelfish are tropical fish and prefer water temperatures in the range of 76-82 degrees Fahrenheit (24-28 degrees Celsius).
  • Guppies: Guppies are also tropical fish and prefer water temperatures in the range of 76-82 degrees Fahrenheit (24-28 degrees Celsius).
  • Tetras: Tetras are tropical fish and prefer water temperatures in the range of 76-82 degrees Fahrenheit (24-28 degrees Celsius).
  • Cichlids: Cichlids are a diverse group of fish and can be found in both coldwater and tropical environments. Some cichlids, such as angelfish and discus, prefer water temperatures in the range of 76-82 degrees Fahrenheit (24-28 degrees Celsius).
    • Other cichlids, such as Texas cichlids and Oscars, prefer cooler water temperatures in the range of 72-78 degrees Fahrenheit (22-26 degrees Celsius).
  • Betta fish: Betta fish, also known as Siamese fighting fish, are tropical fish and prefer water temperatures in the range of 76-82 degrees Fahrenheit (24-28 degrees Celsius).
  • Barbs: Barbs are tropical fish and prefer water temperatures in the range of 76-82 degrees Fahrenheit (24-28 degrees Celsius).
  • Gouramis: Gouramis are tropical fish and prefer water temperatures in the range of 76-82 degrees Fahrenheit (24-28 degrees Celsius).
  • Catfish: There are many different species of catfish, and their temperature requirements can vary widely. Some catfish, such as Corydoras and plecostomus, are tropical fish and prefer water temperatures in the range of 76-82 degrees Fahrenheit (24-28 degrees Celsius).
    • Other catfish, such as channel catfish, are more tolerant of cooler temperatures and can thrive in water as cool as 60-70 degrees Fahrenheit (15-21 degrees Celsius).
  • Koi: Koi are coldwater fish and can tolerate a wide range of temperatures, from about: 60-70 degrees Fahrenheit (15-21 degrees Celsius).

Waste in Fish Tank Water

Waste is one of the factors that can impact the water quality in a fish tank. Fish produce waste in the form of feces, which can release nutrients back into the water if it is not properly managed. In addition, uneaten food and other organic matter that breaks down in the tank can also contribute to excess nutrients in the water.

If the levels of waste and nutrients in a fish tank are not properly managed, it can lead to a range of problems, including:

  • A decrease in the oxygen levels in the water can be harmful to fish
  • An increase in the levels of ammonia, nitrite, and nitrate, which can be toxic to fish
  • A bacterial bloom can be harmful or even deadly to fish if it becomes excessive
  • A decrease in the overall water quality can impact the health and well-being of the fish

It is important to properly manage waste and nutrients in a fish tank by performing regular water changes, using a filter to remove excess nutrients, and properly disposing of uneaten food and other organic matter. This will help to maintain a healthy and clean environment for your fish.


If you are looking to buy a fish, start up a home aquarium, or are unsure why your fish continually are getting sick or dying, it is likely that your water quality is poor. If your water is not at a healthy level, you may be suppressing your fish’s immune system and subjecting them to diseases or even death. 

The first step to knowing how to balance your water to ensure the water parameters are safe is knowing what chemicals to look for and how they impact your fish. By knowing exactly what symptoms to look for in your fish, you will be able to identify when something is off and take immediate action. 

Even if you are not noticing any abnormalities in your fish, it is important to clean your aquarium and check the water health weekly. By knowing exactly what to look for when you evaluate your water quality, you will be able to identify immediately when something is not in balance in your aquarium. 

Whenever you change the water in your tank, be sure to condition it first and check for any imbalances if you want to elongate your fish’s lifespan and avoid any disease development in your aquarium. This will keep the water clear and healthy so that you will be able to see your fish clearly and provide a healthy and clean environment for your fish. 

It is important to regularly test the water in your tank and make any necessary adjustments to ensure that these parameters are within safe ranges for your fish. If you are unsure of the appropriate ranges for your fish, it is a good idea to consult a veterinarian or a knowledgeable fish store employee.

Recent Posts