Ammonia, Nitrite, Nitrate: Reading Your Test Kit

Clear water isn't the same as clean water. A tank can look perfect and still have levels of ammonia or nitrite that are slowly poisoning your fish. A test kit is how you know for sure, and the three tests that matter most are ammonia, nitrite and nitrate.

The nitrogen cycle in one paragraph

Fish waste, uneaten food and dead plants break down into ammonia, which is toxic. Beneficial bacteria in your filter and substrate turn ammonia into nitrite, which is also toxic. A second group of bacteria turns nitrite into nitrate, which is much less harmful and builds up until you remove it with water changes. That's the cycle. See how to cycle a new aquarium for setting it up.

The readings you want

• Ammonia: 0 ppm
• Nitrite: 0 ppm
• Nitrate: low; many keepers aim for under 20 ppm and keep it below 40

Any ammonia or nitrite in an established tank means something is wrong.

Liquid tests vs. strips

• Liquid test kits are more accurate and cheaper per test. You add drops to a tube of tank water and compare the color to a chart.
• Test strips are fast and easy but less precise, and they can go bad if they get damp.

For a new tank, or if fish are sick, use a liquid kit.

How to test without fooling yourself

1. Read the instructions for your kit. Each brand is different.
2. Rinse the tubes with tank water, not tap water.
3. Measure carefully. Fill to the line.
4. Shake reagents if the instructions say to. Some nitrate tests need a reagent bottle shaken hard, or you'll get a falsely low reading.
5. Wait the full time before reading the color.
6. Read in good light against a white background, holding the tube next to the chart.
7. Check expiration dates. Old reagents give wrong results.

Test before a water change, not right after.

What to do if a number is high

Ammonia above 0

• Do a water change of 25 to 50 percent with dechlorinated water at the same temperature.
• Cut back on feeding.
• Look for the cause: a dead fish or snail, rotting food, too many fish, or a filter that was cleaned too hard.
• Don't clean the filter with tap water. Chlorine kills the bacteria you need. Rinse filter media in old tank water.

Ammonia is more toxic at higher pH and temperature, so a small reading matters more in warm, hard water.

Nitrite above 0

• Water changes, as above.
• Common in tanks that are still cycling or had a disruption.

Nitrate climbing

• More frequent water changes. See how often to change aquarium water.
• Feed less.
• Add live plants, which use nitrate.
• Check your tap water. Some tap water already has nitrate in it.

Other tests worth having

• pH (see adjusting pH in a riparium)
• General hardness (GH) and carbonate hardness (KH), important for snails and shrimp
• Temperature, every day

How often to test

• New tanks: every day or two during cycling.
• Established tanks: weekly, or any time fish act strange.
• After adding fish, for a couple of weeks.

Testing takes five minutes and catches problems before your fish show them.

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