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What to Test for in your Freshwater Aquarium? Full Answer

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Freshwater aquariums are absolutely beautiful and can house some pretty fantastic fish and plants. However, having a freshwater tank doesn’t come without a bit of work. 

Testing your water parameters for ammonia, nitrite, nitrate, pH, water hardness, carbonate hardness (KH), phosphate, copper, and chlorine is essential for keeping your freshwater tank healthy. In established tanks, tests should be done monthly, except in a few circumstances. 

Testing these parameters is simple with the help of a few testing kits, but it is important to know why each of these elements is harmful to your freshwater aquarium and what the levels should be.

pH test aquarium


Typically, the ammonia level in the tank should stay at a consistent 0 ppm (parts per million). This means that there ideally shouldn’t be any ammonia in the tank, as it is extremely toxic to fish.

While it may be a contradiction, fish actually excrete ammonia in their waste. This makes it crucial to ensure your freshwater aquarium is cleaned accordingly with proper filters, a schedule for partial water changes, along with a few bottom-feeders and live plants if possible.


Similar to ammonia, nitrite should also be at a 0ppm. In an established freshwater aquarium, beneficial bacteria (in a tank that has been cycled) consume the ammonia and produce nitrite. However, this doesn’t neutralize ammonia. Instead, it remains toxic to fish and can cause their skin and gills to burn. 


While they are similar in name, nitrite and nitrate are a bit different and both should be tested when it comes to your water parameters.

There are several types of beneficial bacteria in a tank when it is established and one of them consumes nitrite and turns it into nitrate!

As you can probably tell, there is a specific cycle that forms when having an established aquarium. Nitrate is not as toxic to fish as ammonia and nitrite, but it should still be kept to a minimum. 

On average, the nitrate level should be 50 ppm or below. Keep in mind that aquarium plants feed off of nitrate so you will want to ensure there is at least 20 ppm in the tank to keep them healthy. 


The pH in a tank is basically how acidic or not the tank is. The average pH for a freshwater tank should remain between 6.5-8.0. Of course, this ranges depending on what species of fish you have in your tank as well. 

If you do notice that your pH is off balance and higher than recommended, you can do a partial water change to combat this while adding a chemical balancer found at most fish stores.

Water Hardness

Water hardness in a tank usually doesn’t bother fish or plants. However, there are a few species that can be thrown off by water that is too hard. Water hardness is overall detected by the minerals present in the water. Of course, fish need minerals.

With that being said, most freshwater aquariums should have a water hardness measured between 4-8dGH.You will want to ensure that this holds true for any special fish or plants you may have.

Carbonate Hardness (KH)

As mentioned, a high pH can throw off your aquarium and the carbonate hardness of a tank combats this issue. The KH acts as a cushion in the water to prevent the pH from fluctuating constantly. 

In other words, the higher your KH in the tank, the less likely the pH will change, which can keep your fish from getting sick or stressed.

It is recommended to keep your KH levels at around 50 ppm or above for maximum benefits. 


Phosphate is a nutrient that aquarium plants need to feed off of to thrive. With that being said, there is a point where there is too much phosphate.

At that point, this nutrient causes further algae growth. This is where algae blooms come in and your freshwater aquarium will start to turn green.

Typically a tank should have a phosphate level between 0.5-3.0 ppm There are phosphate test kits that will help you keep these parameters in check.

It is important to note that low-lighted tanks should have a phosphate level on the lower end of the spectrum, while highly-lit tanks should be on the high end of the spectrum. 


Copper doesn’t necessarily hurt your fish, in fact, it is commonly used in medicines for fish to fight a few common diseases. However, if you have any freshwater invertebrates in your tank, copper can be a problem. 

Small shrimps and snails are commonly used in tanks as “cleaners”, however, they can be sensitive to even the smallest amount of copper.

With that being said, you will want to test the copper in your water prior to using it for water changes, and after applying medicine to your fish if needed. 


Chlorine is found in all tap water as an additive, but it is detrimental to your fish. For some fish, it may take only a few minutes to pass away from chlorine, but for others, it can take up to two days. You will notice that your fish are gasping for air due to a lack of oxygen.

In order to combat this, you can get a dechlorinator at any local pet store. As you’re adding the water you add the solution and it will neutralize the chlorine.

If you do not have access to this solution, you can allow your tap water to set for at least 48 hours prior to adding it to the tank.

When to Test the Water in your Freshwater Aquarium

All of the above components can be tested with testing strips found at any local pet store or online. With that being said,  it is important to know when you should actually test the water. 

You do not need to test on a daily basis (unless there is something wrong with a fish), but there are a few circumstances where you should test your water parameters more often. 

  1. You are cycling a new aquarium. If you are in the process of cycling a brand-new aquarium, you will want to test more frequently to ensure levels are where they need to be prior to adding any fish or plants. At first, you will want to test every three days, and then gradually decrease the timespan between testings to every week and then every month.
  1. You are completing tank maintenance. A general rule of thumb is to check the water parameters every time you do a partial water change or any maintenance on the tank such as cleaning the filters. You will specifically want to test ammonia and nitrites since they are overall the most toxic in a tank. 
  1. You have a sick fish without a known cause. If you notice a sick fish in your tank with no obvious cause of death (such as getting stuck in a filter) you will want to test the parameters to ensure there was not an unhealthy amount of ammonia in the tank. On another note, dead fish release ammonia immediately and you will want to watch the levels in your tank after the removal of the fish.
  1. You notice unhealthy plants. If you notice unhealthy plants, such as wilting or brown spots, this could be a sign that the water parameters are off in your tank. You will then want to test your tank and see if a partial water change is necessary.