Don't add fish too soon!
For new aquaponic growers, the temptation to throw fish into a new system can be strong. As we've seen over the years, however, it's worth waiting to add fish to your system.
Adding fish to a new system without waiting can cause serious fish stress and could even result in fish death. We've seen growers spend weeks trying to stabilize their system because they got too eager and added fish too soon.
Instead, get your system running first and let the microbe populations establish.
How long do you have to wait before adding fish to a system?
On every new system you have to wait until you are cycled. In colder climates getting cycled can take as much as eight or ten weeks. Some folks in warmer climates, on the other hand, can cycle in four weeks. This difference in timing depends on the biological surface area of your media.
You can also speed up cycling processes by inoculating your system. To do this, get a water sample or media sample from another healthy aquaponic system (or another body of water) and add it to yours. (This is sometimes called live water.) This will jumpstart the cycling process.
The caveat to inocculation is that you want to make sure that it is coming from a healthy body of water or a healthy system. If it is coming from a system with diseased fish then you can run the risk of introducing disease.
How to tell if your system is cycled
Once your water measurements show up at the level that you want to keep them, then your system is ready. For most aquaponicists, the measurements look like this:
Ammonia: Less than 2 ppm
Nitrites: Less than 1 ppm (ideally less than .5 ppm)
Nitrates: up to 160 ppm
If your numbers are off the chart high or low, I highly recommend remeasuring. Dozens of "problems" that growers have with their nutrient levels are actually measuring (or measurement reading) issues.
Everything look good? Then you're ready to add your fish.
Cycle your system for six weeks before adding fish to it. Once ammonia levels are low enough and nitrates are high enough, you can add the fish. And don't forget to remeasure if something looks off.