How To Read Water Test Strips for Fish Tank?

Whether you’re an aquarium newbie or aquatic expert, you’ll want to know that your fish tank’s water is safe and balanced correctly for your marine life. Poor water quality is one of the main causes of fish distress or illness and can often lead to their death if left unchecked.

It’s important to test your aquarium’s water regularly, therefore, to ensure it is suitable for your particular fish. Unfortunately, water that could harm your fish will look exactly the same as that which is ideal. While it can be easy to spot dirty or unfiltered water, there are some key factors that are essentially indistinguishable without adequate tools.

One of the cheapest and easiest ways to test the quality of your aquarium’s fish tank is with water strips.

In this guide, we will explain how to read water test strips for fish tank owners, detailing their accuracy and answer some commonly asked questions.

What is a Water Test Strip?

A water test strip is a commercial product for measuring the levels of key markers within a fish tank. These markers can help determine the overall health of an aquarium and allow owners to plan measures accordingly.

The strips are inexpensive and can be bought from most aquatic stores. They most often come in packs of 25 but can be found in larger quantities if you will be conducting a lot of water testing.

The strips themselves look similar to litmus paper but with protruding square pads along its length. These individually test the levels of different elements of the water’s composition. Most strips will feature 5 of these pads and test for the following:

• General hardness
• Carbonate hardness
• pH level
• Nitrite level
• Nitrate level

While most water test strips measure these 5 elements, there are other products that feature additional pads for extended testing. For most aquarium owners, however, the 5-in-1 test strips are the most useful. These test for the most important hallmarks of a healthy tank and extended test strips are often unnecessary unless keeping highly sensitive fish and plant life.

The strips are single use so once they have been used should be appropriately discarded.

How to Use Water Test Strips For An Aquarium in 4 Steps?

Using a test strip is easy, but it’s important to follow instructions carefully to get a clear reading:

1. Take a sample of your tank’s water

Using a thoroughly cleaned plastic or glass test tube or suitable vessel, scoop out a small sample of your aquarium’s water.

Be mindful not to disturb your fish or cause undue distress during this process.

While you can dip your strip directly into your tank, it is recommended to isolate the water first and let it settle in the container to get the most accurate reading.

Some test kits come with a test tube for drawing samples of water, the packaging will indicate if this is the case.

2. Place the strip in the sample

Next, simply place the test strip into the test tube submerging it into the water.

You want to ensure that none of the pads is making contact with the inner sides of the test tube or this can affect the results.

Importantly, make sure all of the pads are submerged. Unlike litmus paper, which test strips resemble, the tip of the paper alone is not enough. All 5 (or more) of the square pads should be fully sat in the water itself.

3. Remove the strip and wait

Wait 5-10 seconds and then remove the strip carefully, ensuring the square pads do not make contact with the test tube.

While it can be tempting to give the strip a final stir before doing this, you risk invalidating the results if it makes contact with residue on the inner surface of the glass or plastic.

4. Compare the result

Once you have carefully removed the strip you will notice the square pads begin to change color.

The color of these pads can then be compared against the color chart provided with your strips.

For example, the pH pad on your strip will shift towards red the more acidic it is. How acidic depends on the shade of red which can be compared using the chart.

Each brand of water test strip will have its own color chart with minor differences therein. It is important then to only compare the results to the chart that comes with the original packaging.

Understanding the results

While it can be a little confusing at first, understanding the results of your test strip is relatively simple:

General Hardness (GH)

The first pad nearest the “handle” end of the water test strip typically measures the general hardness of your tank’s water, GH for short.

This is a measure of the salt content of your water, chiefly calcium and magnesium Ions. Soft water means a low content, hard water features a large amount.

Most tank owners need not worry about this measure as fish are great at acclimatizing to both.

Carbonate Hardness (KH)

The next pad measures the carbonate hardness of your water (KH). This tests the dilution levels of carbonates (CO3) and bicarbonates (HC03) in the aquarium’s water. This is also referred to as “alkalinity” which is the term used to determine the anti-acidifying effect of your water’s makeup.

These help keep the pH level of your tank in check. If the KH level of your tank is too low, it can create an overly acidic environment.

pH level

Different kinds of fish require different pH levels. While fish are not as sensitive to pH levels as some owners think, there are some high-maintenance varieties that require quite specific conditions.

The pH pad on your test strip will change color depending on the alkaline (base) and acid level of your tank.

Nitrite level (NO2)

Nitrites build up due to fish waste and plant decay. These can create an unhealthy and potentially toxic water environment as nitrite begins to form. It tends to only occur with new tanks however as, after a period of about 3 to 4 weeks, bacterias develop that help neutralize this compound.

For new tanks especially, it’s important to keep an eye on this measure and ensure it is going down over time.

Nitrate level (NO3)

Nitrate is the neutralized form of nitrite. It is generally not toxic to fish in the quantities found in aquariums and if your test strip shows it is detected you can be sure you have the right kind of bacteria present in your aquarium.

Frequently Asked Questions

Are aquarium test strips any good?

Used correctly, water test strips can be a cheap way to get an idea of your aquarium’s overall health. While there is room for error in judging the shade of color, these strips give a good indication of the various levels within your tank.

However, some owners prefer dedicated single marker testing kits to ensure they get the most accurate result.

This way you don’t need to use an entire test strip to simply test the pH level, for example.

What are some alternatives to test strips?

Owners with high-maintenance fish often prefer master test kits. These kits require owners to add various solutions to samples of water and compare the resulting change in water color. These are more accurate but take longer to perform tests.

How long do water test strips last?

Test strips can go out of date and can be affected by air moisture. It is important then to keep them in a water-tight container to get the most accurate results. Most test strips will last for at least 2 years if stored correctly, with the packaging indicating the expiry date.