> closed-loop hydroponics

Aquaponics?

I guess; I didn't realise there was a difference in the terms.

Hydroponics and aquaponics are both considered closed-loop (compared to other agricultural methods). Hydroponics involves growing plants.

If you're raising fish in addition to crops in your system, with the fish excrement providing the nutrients the crops need, then you're engaged in aquaponics.

It's not really closed-loop though, is it? You still need to buy food to feed the fish (and maybe fish food, which will end up in your vegetables, can be contaminated, e.g. with heavy metals?)

Or am I missing something?

Those closed systems involve growing algae which is used to feed the fish.

> closed-loop hydroponics

Aquaponics