Keeping the balance: feeding, pH, temperature
The fish are calm, but the plants look hungry. What would you change?
My leaves look pale. Is there enough food in the water?
Think of a seesaw. Fish sit on one end, and plants sit on the other.
The food you scoop in is the weight that tips it.
More fish food means more fish waste. The crew turns that waste into plant food.
So a little more food can feed hungry plants.
Food the fish don’t eat rots in the water. Rotting food makes ammonia, which stresses fish.
So feed only what the fish eat in about half an hour.
Plants like the pHA number that tells you how sour or how soapy water is.
See it in the glossary a bit sour. Fish and the crew like it a bit higher.
So growers aim for the place they meet, about 7.
- A · plants
- B · fish
- C · bacteria (the crew)
- D · meeting point
The crew’s work slowly makes the water more sour, so the pH drifts down.
Growers check it often and nudge it back up.
Cold water slows the crew down. Many fish eat less, so there is less plant food.
That is why growers pick fish that suit their water, or warm the water.
Your turn: keep the seesaw level.
Keep the fish calm and the plants growing for 7 days.
Day 0Days in balance: 0 of 7
Keep the fish calm and the plants growing for 7 days.
- Ammonia: Low
- Nitrate: OK
- Fish: Calm
- Plants: Growing
| Setup | What happens |
|---|---|
| Too much food5 fish, Heavy food, 2 plants | The fish get stressed, and nitrate builds up, with too few plants to use it. Ammonia builds up. |
| Too few fish1 fish, Light food, 6 plants | The fish stay calm, and the plants are hungry. |
| Balanced4 fish, Normal food, 5 plants | The fish stay calm, and the plants keep growing. |
Real growers change one thing at a time. Then they wait and watch.
That way, they know which change made the difference.
Check 1 of 3
You feed the fish much more than they can eat. What happens?
Show the answer
Leftover food rots and makes ammonia. Right. Rotting food adds ammonia, and too much ammonia stresses the fish.
Check 2 of 3
Why do aquaponics systems run at a higher pH than hydroponics?
Show the answer
The fish and the crew like it higher. Right. Plants like it a bit sour, so growers meet in the middle, near 7.
Check 3 of 3
The fish are calm, but the plants look hungry. What could help?
Show the answer
Feed the fish a little more, slowly. Right. More food means more waste for the crew to turn into plant food. Go slowly and watch.
You just learned how food, pH, and temperature keep fish and plants in balance.
Go deeper: feeding rates and buffersOpenClose
Growers often size a system by how much fish food goes in each day for each square meter of plants.
One guide suggests about 40 to 50 grams of feed a day per square meter for leafy greens. It suggests 50 to 80 grams for fruiting plants.
Guides for floating-raft beds suggest more, about 56 to 100 grams. The numbers differ, partly because systems differ.
Many guides say to feed only what the fish eat in 20 to 30 minutes, then take out the rest.
When the crew turns ammonia into nitrate, it releases acid. That is why the pH of a running system slowly falls.
To raise it gently, growers add small amounts of a buffer, such as crushed shell or a little calcium or potassium carbonate. These also add calcium or potassium for the plants.
In cold water, many fish eat less, which means less waste and less plant food. The crew also works more slowly.
Each bar on the pH chart shows a range that partner can live with. Plants grow best near 6 to 6.5, and the crew works fastest above 7.
Guides pick slightly different meeting points, from about 6 to 7.5. Many aim close to 7.
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
- 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
- Mullins, C., Nerrie, B., and Sink, T. D. Principles of Small-Scale Aquaponics. SRAC Publication No. 5007. Southern Regional Aquaculture Center, September 2015. 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
- Francis-Floyd, R., Watson, C., Petty, D., and Pouder, D. B. Ammonia in Aquatic Systems. FA16. UF/IFAS Extension, University of Florida. Link
- Chappell, J. A. Nitrite Poisoning or Brown Blood Disease: A Preventable Problem. Auburn University, 2008. Link