[ctrlaltesc]

You still have to feed the fish, so it's not really closed. But it is reasonably self-contained in combination with using vegetable waste to breed fly larvae which go on to feed the fish.

The difficult thing about aquaponics is the cyclomatic complexity (to use a software term). Basically everything feeds into everything else. At first you might think that the system is in balance, but in fact it rarely is. Plants and fish will be added and removed regularly, each agent having different nutritional needs at different stages in their lifecycle. Disease or infestation of plants or animals can be difficult to deal with, as any pesticide or herbicide will cycle through the complete system. There simply aren't any cheap off-the-shelf sensors to monitor things you care about, so you need to do regular physical checks with chemical kits.

Aquaponics is a fun, but very hard, problem to solve correctly. You can learn a lot from it, and it is a great system for people who like to learn a bit about everything.

[delinka]

Allow me to nitpick about physical checks with chemical kits-- I'm sure we can build a sensor for that. The potential problem I see, however, is that by the time you detect a dangerous chemical change, it's too late. Visual inspection is still important (to see that Nemo's gimpy fin is caused by an infection rather than a birth defect) until we figure out AI enough to detect certain kinds of things.

[etcet]

I've heard that you can add another tank between the plants and the fish where you can grow algae that feeds the fish.