How To Test For Aquarium Nitrate: The Complete Guide

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While most fish owners know that toxins like nitrate can be dangerous, not everyone knows how to test for it or how often to do so. Therefore, I decided to gather everything I know about this topic into one article.

You can test your aquarium for nitrate by using a test kit. Most fish owners use testing strips as they are quite affordable, although liquid test kits are prevalent as well. You can also bring a sample to a fish store and get a professional interpretation of the results.

As we move forward, I’ll elaborate on the different options you have if you wish to test your water for nitrates. Then, I’ll discuss which option works best and what are acceptable nitrate levels.

How Can I Test My Aquarium For Nitrates At Home?

Nitrates are inevitable, not just because Nitrosomonas bacteria in an established tank convert ammonia into nitrates daily. 

The substance is an oxidized form of nitrogen.[1] You can find it in various water sources because of exposure to fertilizers, runoff from farms, pollutants from factories, and the like. 

Therefore, you should test new water for nitrates before adding it to the aquarium. You have four primary testing options at your disposal:

1. Send A Sample To A Lab

Besides educating people about the awareness of nitrate contamination, the Minnesota Department of Agriculture introduced a testing program in the 1990s that simplified access to testing services.[2]

Today, laboratory testing services are all the rage. That makes sense because an accredited lab can provide more accurate testing services than the many testing kits people use at home.

Additionally, these services are convenient because you don’t have to abandon the comfort of your home to identify nitrates in the aquarium. 

The most challenging task is collecting a sample of water in a vial. Pack the sample and ship it to your lab of choice. You can expect feedback within 24 hours, depending on the efficiency of the lab in question.

2. Use A Liquid Test Kit

Liquid tests are a decent alternative if you don’t have access to a lab or you don’t want to wait. Brands like API offer products with multiple bottles that test everything from ammonia to nitrites and nitrates.

Although, you can buy cheaper kits that only test nitrates. Then again, aquariums are vulnerable to various toxins. It is more cost-effective to buy a liquid test that targets multiple substances. 

An excellent example of such as kit is the well-known API FRESHWATER MASTER TEST KIT (link to Amazon). That is also the kit I use to test the water in my fish tank.

A liquid test kit is one of the best ways to test aquarium water for toxins.

3. Purchase Testing Strips

Testing strips are popular because of their convenience. They are the simplest at-home testing tools you could ever use. The kits include instructions that any layperson can understand. 

Additionally, testing strips are cheap. As such, you can test your water as frequently as you want without going bankrupt. After all, you can get 25 strips for as little as $10.

An obvious example would be the API 5-in-1 Test Strips (link to Amazon). These will test your water for nitrates and nitrites and will measure the pH and hardness levels.

4. Pick A Sample To A Fish Store

There’s a significant difference between sending a sample of aquarium water to a lab and a local fish store. 

A lab will use the latest technology to analyze every aspect of your sample. Your local fish store is just as likely to use a testing strip to scrutinize your sample.

This is why some fish stores offer free testing services. They use the same at-home testing tools you find in the homes of most aquarists. 

Their services appeal to newcomers that don’t know how to test aquarium water for nitrates, let alone how to interpret the results.

5. Commercial Tools

The market is saturated with devices that test for nitrates. That includes handheld TDS meters, water testing kits with photometers, chemistry sets, etc.

Some commercial tools test for nitrates and nothing else. Others will scrutinize every significant variable in the aquarium. 

How Do I Use A Nitrate Test Kit?

The most common testing tool is a testing strip because of the simplicity it brings to the table. The process of using a testing strip involves the following:

  • Collect a sample of aquarium water in a container.
  • Retrieve a testing strip and dip it in the water. Make sure the strip is sufficiently soaked.
  • Hold the strip next to the label on the bottle and compare the colors. 

If all that sounds confusing, here is an excellent video that will walk you through it:

Some kits have a separate color chart. The instructions may encourage you to wait several seconds to a minute before comparing the color on the strip to the chart.[3]

The chart will show you how to interpret the color on the strip. The liquid test follows a similar pattern. You need a sample of aquarium water in a vial or container. 

However, rather than dipping a strip in the water, you add several drops of a chemical that came with the kit.

If the kit specifically targets nitrates, you can use any bottle you encounter. However, if the kit tests for multiple substances, look at the labels. 

For instance, you may find one bottle that tests for nitrates and another that looks for ammonia. 

You don’t want to confuse the bottles because you will make the wrong observations. For example, you risk confusing the ammonia readings for nitrates. 

Either way, the goal is for the aquarium water sample to change color. Compare the color change to the chart. Conventional aquarists rarely stray beyond these two testing options. 

What Is An Acceptable Nitrate Level In Aquariums?

This 2018 review (International Journal of Environmental Research and Public Health) found a connection between nitrates in drinking water and thyroid disease.[4]

If nitrates in drinking water can cause severe harm to the human body, what do you think they will do to your fish once you add that same water to your aquarium during a water change?

The only way to protect the fish is to keep the nitrates below toxic levels. But you can’t do that unless you know the acceptable nitrate levels in an aquarium. For the most part, fish can survive in any tank with 20 ppm of nitrates.

Nitrates are not like ammonia. Ammonia is so toxic that you have to keep the concentration of the substance at zero to maintain the health of your fish. 

People cycle their tanks because they want to introduce bacteria that change ammonia into nitrites nitrates.

Because nitrates are less toxic than ammonia, and plants consume the substance, your fish can thrive in the presence of low nitrate levels. 

But aquarists have different interpretations of what counts as low nitrate levels. For some people, 50 ppm is perfectly acceptable. For others, 20 ppm is too high. 

You are better off aiming for 10 ppm or less, especially if your aquarium has an algae problem.[5]

What Should I Do If The Nitrates Are Above 20 ppm?

If the nitrates are higher than 20 ppm, the first thing you should do is check for ammonia. That is because nitrates form from ammonia via the nitrogen cycle, and the latter is far more toxic.

In case the ammonia is higher than 0 ppm, I suggest performing a large water change of approximately 30 to 50 percent.

Then, clean the substrate with an aquarium vacuum cleaner. That is the most important step as this is where rotten leftovers hide.

You can easily do that with products like Laifoo 5ft Aquarium Siphon Vacuum Cleaner (link to Amazon). That is the one that I use and I couldn’t be more satisfied.

I also suggest checking this article, where I discussed how to deal with an ammonia spike. Even if the ammonia is at 0 ppm, it is worth knowing what to do in case the situation deteriorates.

Avoid cleaning the filter media as it contains essential bacteria.

How Often Should The Aquarium Be Tested For Nitrates?

You should perform water changes every week without fail. But you can’t add new water to an aquarium without testing it. The last thing you want is to introduce toxins like ammonia, lead, and nitrates to the aquarium.

Therefore, you should test and then purify the new water to ensure that it is conducive to your fish’s health. In that regard, it makes sense to test for nitrates every week. 

You can also use conditioners to make tap water suitable for fish. That is where products like Seachem Prime (link to Amazon) enter the picture.

Bear in mind that a water conditioner doesn’t actively remove ammonia. Rather, it binds to the toxin and neutralizes it. The same goes for nitrates and nitrites.

If you use a water conditioner for your tap water, you don’t have to test it each time. In that case, I would test the water in the aquarium after the water change, to see that everything is okay.

Cleaning plants from debris and leftovers should be done every week.

Pro tip: Dealing with ammonia is key when you find high nitrate levels in your tank. Here is an article with all the information you need about ammonia, including the specific products I use to remove it.

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You don’t have to spend a lot of time or money if you wish to test your aquarium water for nitrates. You can simply get a few testing strips that reveal the results within minutes.

Most kits come with a comprehensive color chart that tells the precise nitrate, nitrite, and ammonia levels in your fish tank.

As for the frequency, I suggest testing the water each week during a water change. It is also essential to test the tap water as it may contain contaminants dangerous to fish.

Generally, fish can tolerate levels of up to 20 ppm nitrate, although it is better to keep it below 10 ppm. Water conditioners are an excellent solution if you found traces of this toxin.