Field Guides & Resources

The idea, in plain words

Container 1 is the fish tank. Container 2 sits above it as a grow bed full of clay or gravel. A small pump lifts dirty water up; bacteria in the media turn fish waste into plant food; the plants drink it and the clean water flows back down by gravity. The honest beginner path is staged: run it as plain hydroponics for two weeks to learn the plumbing, then add hardy fish.

• Cost: ~€150–600 to build · ~€5/month to run.
• Start crops: lettuce, basil, mint, kale, chard.
• Start fish: goldfish or carp (avoid tilapia in Norte PT).

How to build it

1. 1Clean a food-grade IBC (~1000 L) for the fish tank, and cut a second container into the grow bed.
2. 2Mount the grow bed above the fish tank so clean water can return by gravity.
3. 3Fit a submersible pump (buy one rated ~2500 l/h) to lift water tank → grow bed.
4. 4Add a solids filter, then fill the grow bed with clay/gravel media — this is also your biofilter.
5. 5Set up flood-and-drain with a bell siphon (or a simple timer).
6. 6Add an air pump + air stone so the fish always have oxygen.
7. 7Fit an overflow back to the tank and a low drain valve for cleaning.
8. 8Cycle the system fishless for 4–6 weeks, then add hardy fish (goldfish/carp). Start at half stocking.