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Tips on Reading Aquarium Water Tests


Everyone with an aquarium ought to know their water conditions to ensure their animals are living in the best environment possible. That’s why there are test kits for aquariums; whether you use strips or liquid droppers, such tests give readings on chemicals in your tank’s water. You should first familiarize yourself with what these chemicals are and what their readings mean.


Extremely toxic and produced from fish waste and decay

Means water isn’t cycled

Should always read zero


Very Toxic. A by-product of ammonia after being digested by good bacteria

Usually means water is halfway through cycle; cycle not complete

Should always read zero


A little toxic. A by-product of nitrites after being digested by good bacteria

Either means cycle is complete or there are nitrates in the tap water (test tap)

Should stay below 40ppm; better to perform water change at 20ppm


The measure of the acidity or alkalinity in the water.

Low pH usually means water is soft (acidic) while high pH is hard

Most species like pH 6.5—7.5, near 7 (neutral), but stability is more important than a set number.


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Carbonated hardness

High KH usually means higher, stabilized pH. Low KH means pH is likely to swing.

Most fish prefer 80-120


General hardness

High GH means hard water with a lot of calcium and magnesium. Low GH means low minerals.

Most fish prefer 60-120

Ammonia, nitrites, and nitrates have to do with the nitrogen cycle and are regarded with higher importance than the other readings. PH, KH, and GH have to do with the level of softness/hardness and its stability; fish in general can tolerate a wide range of pH, but fluctuating pH can kill. Always research your species’ pH tolerance as some species cannot live in acidic water while others have to.

Now that we got the basic readings out of the way, let’s get to the testing. While test strips are cheaper and much more convenient than liquid tests, they tend to be less accurate on their readings. Also each packet only holds 4-6 test strips (which is why they are so cheap) while the liquid test kits can be used well over 100 times, so in the long run liquid tests are cheaper. So it’s encouraged to rely on liquid test kits instead, although they are a bit more work and testing has to be precise.

Liquid Tests: Is It Yellow Or Yellow-Green?

The shading of a color isn’t so difficult to tell. Just merely place the tube in front of the white part on the chart once the test has been completed. But when you can’t tell the color, such as the ammonia test in the API Water Test Kit, then that is problematic. So how do you determine what the color is if you can’t tell by placing the tube in front of a white background?


Most likely it is the lighting that is causing the problem. Every time I test for ammonia, I cannot use my kitchen light as a light source; it adds green to the test water every time. So it is important to use a reliable light source. If you know that your water has to be ammonia-free (therefore yellow), try placing it under different lights in your house. Bright white (non LED) flashlights are often a reliable source, as well as sunlight.

Point of View

Sometimes looking through the side of the test tube isn’t enough, because the color is too transparent. Making the color denser will often reveal its true color. Instead of looking at it lying on its side, set the tube upright on top of bleach-white paper or on the chart itself. If you look at the surface at an angle, the color should be a darker shade, and therefor easier to determine. If it looks like urine, then it’s ammonia-free. If it has a mossy shade to it, then ammonia is present.

If after all of this you still cannot determine if there is green in the water, odds are there is the tiniest amount of ammonia in there; so small that it looks like it could be ammonia-free. If you aren’t sure, why take a chance? Go ahead and perform a partial water change using an ammonia detoxifier (such as Prime). If the problem is reoccurring, it either means your water isn’t cycled or you are botching your own tests. Here are some suggestions on improving water testing accuracy.

Test Tube Contamination

If you are about to reuse a test tube, don’t merely dump the tested water out and pour the tank water in. The remaining tested water will mess with your results. You also want to make sure none of the solution gets into your tank.

But you don’t want to wash it out with tap water and pour tank water in either; the chlorine in tap water can also mess with the results, not to mention some tap water have traces of ammonia in it. So there are two options: let the tube air dry after washing it under the tap, or the more convenient way, wash the tube (including the cap) with tap and then wash with the tank water you are about to test. This way you are solely testing your tank water, as it should be.

Every Drop Counts

Some of the droppers can be quick while you hold them vertically and squeeze out the drops as instructed. It’s easy to lose count if rapid. That’s why instead of holding it vertically, hold the bottle at a slant so the drops aren’t so quick.

It’s also easy to accidentally miss your target and have a drop climb down on the glass, and sometimes you can’t tell if it’s on the inside or outside (since the outer walls are often wet from reusing). I find it best to just hold the tube while adding the drops. Then when you’ve squeezed the last drop, quickly pull it upright, avoiding accidental additions.

*Sometimes a drop will just linger at the end of the bottle when you are done adding drops. Don't waste it. Suck the drop back into the bottle by squeezing the hard, narrow sides of the bottle (for API).

The 5 ml Line

Another thing that can be aggravating about the liquid tests is getting the measurement right. Just like how every drop of the testing solution matters, so does the test water, and getting it just right on the line can be a challenge. Some would suggest using a no-needle syringe or droppers you can buy in stores. They can certainly help (especially for taking some water out if it’s just over the line), but I have found it to be so much easier to use the caps to accurately add drops of water. Once you’ve dunked the test tube in the water a few times, getting it somewhere under the line, just fill the cap with tank water and slowly add drops until it reaches the line. This way you are not dependent on a separate item; the tube and cap go together, so they will always be together for your convenience.

Mixing Right

It’s suggested to shake the test tube for five seconds after adding all of the solution to the water. Not only does this mix the solution, but it also collects any water that is in the cap. Some tests have to be shaken up to a minute, such as the case with nitrate. Unfortunately the caps on the test tubes aren’t always airtight, and if you’ve ever shaken a test tube and then noticed the water is under the line, it means you are losing water (hard to notice if your hands are wet from the beginning).

This can also affect your result, because you may be losing drops of water before it actually mixes. A gentler way to mix the solution and water is to hold the test tube between your thumb and finger. Gently rock the tube back and forth, forcing water to go up into the cap and back down to the bottom. By violently shaking the cap, you lose a lot of drops, but this gentler way decreases the amount of drops lost.

Test Strips: Is it Orange or Red? It’s Pink

As convenient as the test strips are, they are sometimes hard to read. When people say the test strips are inaccurate, I think they really mean that the results can be inconclusive; therefore you have to guess what pink means when it should either be orange or red. Or what it means when the square is blue on the inside and green on its corners.

Dip It Right

Test strips are pretty straight forward. Just follow the directions. Some people make the mistake of simply dipping the test strip into the water and yanking it out, but often it is instructed to pull them out of the water horizontally with the squares facing up.

Read at the Appropriate Time

People may also read the results too soon or too late. Some squares need to wait 30 seconds. For those that are instant, record them immediately, because their colors will change and no longer be accurate.


If dealing with the pink question, I have found that pink usually means red. If there was any yellow in it, I’d be orange. So when using the API test strips for pH for example, pink means high pH; but how high, I can’t say. As for the color in the middle verses the corners of the square, the middle color is often the accurate one, because most of the water sitting on the square is concentrated in the middle of it.

If you ever have doubts about the tests’ results, I recommended buying a liquid test bottle for that particular chemical and see if it matches. Then you’ll learn what weird results mean over time.

Again, test strips are straight forward and there’s very little you can do to screw it up, unless you completely disregard that brand’s instructions.

Liquid Tests = more work but more accurate

Test Strips = less work, but hard to read and costly in the long run

When to test for ammonia?

  • Every day for a new, cycled tank (1-2 weeks)
  • When adding more fish to the tank (1 week)
  • When fish are acting funny / looking stressed
  • When nitrates are suspiciously low

When to test for nitrites?

  • Cycling
  • When you suspect your tank is going through a mini cycle
  • When fish are acting funny / looking stressed and ammonia tested zero

When to test for nitrates?

  • Every week if tank is under 6 months old
  • When adding more fish to the tank (1 week)
  • When you suspect it's time for a water change, but not sure

After six months, you'll know when it's time for a water change and won't have to rely on checking nitrates anymore, unless you have been adding and replacing different species of fish after those first six months.


David B. on May 05, 2018:

While pH might not always be important, it can become very important in planted tanks where you are using co2 as it can be a guide to show how much co2 is being placed in the water. It might also be useful to know if you are getting pH swings under other circumstances.

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