Running the system

Cycling the system

Cycling is the process of getting the nitrogen cycle going so the beneficial bacteria can keep everything running and the fish can survive. If something catastrophic happens (a loss of water, or the system being shut down for a while) you may need to cycle again from scratch.

Commercial ammonia is hard to get in Australia, so the method I use is fishless cycling with the "peeponics" approach: adding some healthy human urine to the system every few days, with a small amount of sacrificial plants, and watching the ammonia, nitrite and nitrate levels until ammonia drops off and nitrates appear. This can take a while, especially in winter. Once the system is cycled, fish can safely go in and you can plant out properly.

I recommend cycling without fish wherever possible. It is kinder and it is lower risk.

Yes, it really works, and no, it is not gross when done sensibly. Use basic hygiene: wash your hands, don't splash, and treat it like any other input to a food system you are going to eat from.

pH buffering

When pH drops too low you need to buffer it back up. There are many combinations that work, but this is a cheap, easily available mix of the four elements:

• Calcium carbonate (garden lime): about 20g
• Calcium magnesium carbonate (dolomite lime): about 20g
• Potassium hydroxide (caustic potash): about 20g
• Magnesium sulphate (Epsom salts): about 10g

Add the buffer to the point furthest from the fish (in my system, the end of the sump). Do not keep adding more. Wait a day for the system to settle, measure pH again, and only then add more if you need to.

Mineralisation (free liquid feed from waste)

Mineralisation takes the sludge that collects in the settlement tank and turns it into a free liquid feed for the system. The basic process:

1. Turn off the pump for a short while so any remaining solids settle to the bottom of the settlement tank.
2. Make sure the mineralisation tank's outlet valve is closed.
3. Open the valve from the settlement tank to the mineralisation tank and let it fill from the bottom, to carry as much sludge through as possible.
4. Close the settlement tank valve.
5. Turn on the mineralisation tank aerator.
6. Add molasses (blackstrap).
7. Wait 30 days. The bacteria multiply and break the sludge down.
8. Turn off the aerator.
9. Open the valve from the mineralisation tank to the sump.
10. When the mineralisation tank is empty, close the valve.
11. Clean the aerator and cover the tank, ready for next time.

The maintenance routine

Being proactive and catching things early is the best advice. At the start, keep a close eye on the system; once you know it, some of the daily checks can become weekly.

Daily

• Feed the fish (do not overfeed)
• Test pH (target around 7, can go as low as 6.6)
• During cycling, test all water parameters
• Quick check of the backup system, plumbing, pumps and settlement tank
• Add pH buffer if needed
• Check the auto-siphons are making and breaking properly

Weekly

• Test all water parameters (pH, ammonia, nitrite, nitrate)
• Check fish health more closely
• Test the backup power system
• Water the raised soil beds if they need it
• Check inside the auto-siphons for root growth
• Harvest any fish that have reached a good size (around one a week once the system is established)

Monthly

• Check the settlement tank and run the mineralisation process if needed
• Plan new fish purchases if stocks are low

Yearly

• Check media beds for sludge build-up and refresh gravel if needed (one bed at a time)
• Clean any sludge or algae from tank sides (no chemical cleaners)
• Check and clean the fish tank if needed

Tracking your system

When I first started I logged everything in a Google Sheet. I've since open sourced that as an aquaponics tracker that covers the daily and weekly checks above: water parameters, feeding, maintenance, and the rest. Feel free to use it yourself.

It is built to run on Cloudflare Workers, which suits a simple home tool with no server to maintain. Source and setup notes are on Bitbucket: refactor/aquaponics.

Feeding, the "by observation" method

For a home system, feed by observation. Watch the fish eat, and anything not taken within 20 minutes is too much. Stick with that amount and increase gradually as the fish grow. Do not overfeed; it puts the fish off and creates excess waste. When the fish are small you can grind the pellets down (a coffee grinder works) until they are big enough for full-size pellets.

Stocking density (rule of thumb)

The general home-system rule is no more than 20kg of fish per cubic metre of water. A 1000L IBC holds about a cubic metre, and a harvestable jade perch is around 1kg, so aim for no more than about 20 full-sized fish in the tank.

Minimum fingerling orders are often larger than that (mine was 30), but jade perch grow at different rates, so if you harvest them as they reach size you are very unlikely to ever have more than 20 big ones at once.