Starting a system: why you wait before adding fish
A brand-new system looks clean. Is it ready for fish?
The water sparkles, but something important is missing.
Think of a brand-new restaurant. Before it opens, it hires cooks and trains them.
If hungry customers came on day one, the orders would pile up.
A fish system works the same way. The fish are the customers, and their waste is the orders.
The Recycling Crew is the kitchen crew.
A new system has almost no Munchers or Finishers yet.
If fish moved in now, the ammonia they give off would build up. That stresses the fish.
Many growers feed the crew first, with no fish in the tank.
A pinch of fish food left to rot makes a little ammonia. The crew eats it and grows.
Growing the crew in a new system has a name. It is called cyclingGrowing the helpful bacteria in a new fish system before it is ready for fish.
See it in the glossary.
It takes several weeks, often about a month.
Ammonia rises and falls first, and then nitrite does the same.
Nitrate keeps climbing. In this chart, the system is ready for fish at week 5.
Your turn: when can the fish move in?
Step through the weeks. Add fish when the crew is ready.
Week 0 of 6
Step through the weeks. Add fish when the crew is ready.
- Ammonia: Low
- Nitrite: None
- Nitrate: None
- Fish: Not added yet
- Plants: Hungry
Munchers: A fewFinishers: None
In a new system, ammonia rises first, then nitrite. The crew grows and turns them into nitrate.
Add fish only when ammonia and nitrite both fall to none. Here that is week 5.
Growers test the water to know when it is ready. Ammonia and nitrite read near none, and nitrate shows up.
Then an adult adds a few fish at first, not a crowd.
Check 1 of 3
Why do growers wait before adding fish to a new system?
Show the answer
The crew isn't ready, so ammonia would build up. Right. With too few bacteria, ammonia builds up and stresses the fish.
Check 2 of 3
How do growers know a new system is ready for fish?
Show the answer
Ammonia and nitrite test near none, and nitrate shows up. Right. That means the Munchers and Finishers are both doing their jobs.
Check 3 of 3
About how long does cycling a new system take?
Show the answer
Several weeks. Right. It often takes about a month, and longer in cold water.
You just learned why a new system grows its crew before the fish arrive.
Next up: Choosing fish and plants that get along.
Go deeper: why the lines take turnsOpenClose
Munchers feed on ammonia, so they multiply first. While they catch up, ammonia climbs, then it falls as their numbers grow.
Finishers feed on nitrite, the Munchers’ product. Their numbers rise only after nitrite appears, so the nitrite peak comes after the ammonia peak.
Guides differ on how long cycling takes. A guide from the Food and Agriculture Organization says 3 to 5 weeks, and elsewhere 25 to 40 days.
In cool water, that guide says, it can take up to two months. An Oklahoma State University fact sheet says to allow at least four weeks.
These bacteria work best in water from about 17 to 34 °C (63 to 93 °F). In colder water, they slow down.
Adding some gravel or filter material from a healthy, established system brings living bacteria along. This can start a new system much faster.
The chart on this page is a simple model. Real systems vary, which is why growers test the water instead of counting weeks.
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
- McGee, M. and Cichra, C. Principles of Water Recirculation and Filtration in Aquaculture. FA-12. Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. First published October 1988, reviewed April 2000. Link
- Hargreaves, J. A. and Tucker, C. S. Managing Ammonia in Fish Ponds. SRAC Publication No. 4603. Southern Regional Aquaculture Center, December 2004. Link