When things go wrong: fish, plants, or bacteria?
Why are these fish gasping at the top?
These fish crowd the top of the water. Something in the tank is off.
Something's wrong in my tank. Can you find out what?
Be a detective.
Think of a detective with three suspects.
The detective checks every clue, then names who did it.
Trouble can start with the fish, the plants, or the crew.
They all share one loop of water. So a problem for one can reach them all.
Growers don’t guess. They test the water for ammonia, nitrite, pH, and temperature.
The set of tests is called a test kitA set of small tests that tell you what is in your water, like ammonia and pH.
See it in the glossary.
- A · ammonia
- B · nitrite
- C · pH
- D · water temperature
Is ammonia high? Then waste is piling up.
The Munchers may be behind, or the fish may get too much food.
- A · ammonia
- B · nitrite
- C · pH
- D · water temperature
Is nitrite high? Then the Finishers are behind.
Nitrite piles up faster than they can change it into nitrate.
- A · ammonia
- B · nitrite
- C · pH
- D · water temperature
Low pH slows the crew down. Cold water slows the crew, and many fish eat less.
Either way, the plants get less food.
- A · ammonia
- B · nitrite
- C · pH
- D · water temperature
Your turn. Be the tank doctor.
Open the clues, then pick the cause.
Tank doctor · Case 1 of 6
Gasping in a new tank
The fish gasp at the top of the water. This system was set up one week ago.
Something's wrong in my tank. Let's look for clues.
Clues · tap to check each one
What is the most likely cause?
Tank doctor. Read each case. Check the clues. Then read the most likely cause.
Case 1: Gasping in a new tank
A cutaway of an aquaponics system. A fish tank sits low on the left. 3 fish swim in the tank, gasping near the top: they are stressed. A pump in the tank lifts water up a pipe to a grow bed filled with gravel, higher up on the right, where plants grow. The water soaks through the gravel and drains back down to the tank. Dashed lines mark the top of the water in the tank and in the bed. The fish gasp at the top of the water. This system was set up one week ago.
- AmmoniaLotsHigh
- NitriteNoneOK
- pH7.0OK
- Water temperature24 °COK
Most likely cause: The crew isn't ready yet
A new system has few Munchers. Ammonia builds up faster than they can change it.
A grower would: Feed very little and test every day until the crew catches up.
Case 2: Leftovers on the bottom
A cutaway of an aquaponics system. A fish tank sits low on the left. 3 fish swim in the tank, gasping near the top: they are stressed. A pump in the tank lifts water up a pipe to a grow bed filled with gravel, higher up on the right, where plants grow. The water soaks through the gravel and drains back down to the tank. Dashed lines mark the top of the water in the tank and in the bed. Old food lies on the bottom of the tank. The fish gasp at the top. This system is a year old.
- AmmoniaLotsHigh
- NitriteNoneOK
- pH7.0OK
- Water temperature24 °COK
Most likely cause: Too much food
Food the fish don't eat rots. Rotting food makes more ammonia than the crew can handle.
A grower would: Scoop out the old food. Then feed only what the fish eat in about half an hour.
Case 3: Stuck on step two
A cutaway of an aquaponics system. A fish tank sits low on the left. 3 fish swim in the tank, gasping near the top: they are stressed. A pump in the tank lifts water up a pipe to a grow bed filled with gravel, higher up on the right, where plants grow. The water soaks through the gravel and drains back down to the tank. Dashed lines mark the top of the water in the tank and in the bed. The fish breathe fast at the top of the water.
- AmmoniaNoneOK
- NitriteLotsHigh
- pH7.0OK
- Water temperature24 °COK
Most likely cause: The Finishers are behind
The Munchers made nitrite, but the Finishers can't keep up. Nitrite hurts fish too.
A grower would: Feed less and wait for the Finishers to catch up.
Case 4: Everything slowing down
A cutaway of an aquaponics system. A fish tank sits low on the left. 3 fish swim in the tank. A pump in the tank lifts water up a pipe to a grow bed filled with gravel, higher up on the right, where plants grow. The water soaks through the gravel and drains back down to the tank. Dashed lines mark the top of the water in the tank and in the bed. The plants grow slowly. The ammonia is creeping up a little.
- AmmoniaA littleOK
- NitriteNoneOK
- pH5.5Low
- Water temperature24 °COK
Most likely cause: The pH has dropped too low, so the crew slows down
The crew works slowly when the pH is low. Ammonia builds up, and plants get less food.
A grower would: Raise the pH a little, slowly.
Case 5: Sleepy fish
A cutaway of an aquaponics system. A fish tank sits low on the left. 3 fish swim in the tank. A pump in the tank lifts water up a pipe to a grow bed filled with gravel, higher up on the right, where plants grow. The water soaks through the gravel and drains back down to the tank. Dashed lines mark the top of the water in the tank and in the bed. The fish move slowly and don't eat. The plants grow slowly too.
- AmmoniaNoneOK
- NitriteNoneOK
- pH7.0OK
- Water temperature15 °CLow
Most likely cause: The water is too cold for these fish
These fish like warm water. In cold water they eat less, so the plants get less food.
A grower would: Warm the water, or choose fish that like cool water.
Case 6: Nothing wrong
A cutaway of an aquaponics system. A fish tank sits low on the left. 3 fish swim in the tank. A pump in the tank lifts water up a pipe to a grow bed filled with gravel, higher up on the right, where plants grow. The water soaks through the gravel and drains back down to the tank. Dashed lines mark the top of the water in the tank and in the bed. The fish swim calmly. One old leaf at the bottom is turning yellow.
- AmmoniaNoneOK
- NitriteNoneOK
- pH7.0OK
- Water temperature24 °COK
Most likely cause: Nothing is wrong
Old leaves yellow and fall off as a plant grows. Every reading is OK.
A grower would: Change nothing. Keep watching the fish and the new leaves.
Remember Lesson 14? Change one thing, then watch.
If you change two things at once, you can’t tell which one helped.
One change at a time. Then we wait and watch.
Check 1 of 3
Fish gasp at the top of a system set up one week ago. What is wrong?
Show the answer
The crew isn't ready yet. Right. A new system has few Munchers, so ammonia builds up.
Check 2 of 3
The test kit shows high nitrite. What does that mean?
Show the answer
The Finishers are behind. Right. Finishers change nitrite into nitrate. They can't keep up yet.
Check 3 of 3
Why do growers change only one thing at a time?
Show the answer
So they can tell what helped. Right. Change one thing and watch. If it helps, you know why.
You just learned how a test kit helps you find what went wrong in a tank.
Next up: Project: design a small aquaponics system on paper.
Go deeper: why clues overlapOpenClose
Many problems look alike from the outside. Gasping fish can mean too little oxygen in the water, or too much ammonia or nitrite.
Nitrite gets into a fish’s blood and makes it harder to carry oxygen. That is why high nitrite also makes fish gasp.
Warm water holds less dissolved oxygen than cool water. So a warm tank needs plenty of air.
Ammonia is more harmful when the pH and temperature are high. More of it is in the form that hurts fish.
Many growers also test nitrate. Steady, rising nitrate shows the crew is working and the plants have food.
That is why growers read all the tests together, not one number alone.
Sources
- Somerville, C., Cohen, M., Pantanella, E., Stankus, A. and Lovatelli, A. Small-scale aquaponic food production: Integrated fish and plant farming. FAO Fisheries and Aquaculture Technical Paper No. 589. Food and Agriculture Organization of the United Nations, Rome, 2014. Link
- Deer, C., Hu, B., Dunn, B. and Dusci, J. Nitrification and Maintenance in Media Bed Aquaponics. Fact sheet HLA-6729. Oklahoma Cooperative Extension Service, Oklahoma State University, October 2021. Link
- Mullins, C., Nerrie, B., and Sink, T. D. Principles of Small-Scale Aquaponics. SRAC Publication No. 5007. Southern Regional Aquaculture Center, September 2015. Link
- Rakocy, J. E., Masser, M. P., and Losordo, T. M. Recirculating Aquaculture Tank Production Systems: Aquaponics, Integrating Fish and Plant Culture. SRAC Publication No. 454. Southern Regional Aquaculture Center; Oklahoma Cooperative Extension Service. Link
- Chappell, J. A. Nitrite Poisoning or Brown Blood Disease: A Preventable Problem. Auburn University, 2008. Link
- Francis-Floyd, R., Watson, C., Petty, D., and Pouder, D. B. Ammonia in Aquatic Systems. FA16. UF/IFAS Extension, University of Florida. Link
- Paracueles, C. N. L. Toxicity of Ammonia on Oreochromis niloticus Fingerlings. Journal of Environment and Aquatic Resources, Mindanao State University at Naawan, 2015. Link
- Sallenave, R. Understanding and Preventing Fish Kills in Your Pond. Guide W-105. New Mexico State University, College of Agricultural, Consumer and Environmental Sciences. Link
- U.S. Geological Survey, Water Science School. Dissolved Oxygen and Water. Link