a question regarding big commercial or research systems. Recently I visited the Aquaponic-System of the "IGB - Leibniz-Institute of Freshwater Ecology and Inland Fisheries Berlin e.V..
Instead of growbeds with gravel, they take NFT-Trays with rock wool cubes as the only substrate for the plants. The nitrification takes place in a large biological trickle Filter, where the water runs trough structured plastic-parts. Also the growing vegetables are not in the water circle. The fish-tanks runs with the biofilter run in a primary cycle, but from then, there is only a one way-ticket to the plants. About 5% of water have to be refilled regularly. One of the benefits of this architecture: Additional natural substances or micronutrients can be added indepentently from the fish-water. Cultivating vegetable is fully indepenent tho the bacteria cling to the biofilter, which works very stable at the same level without any maintainance. Even a breakdown of the cultivated plants would not affect the nitrification process.
On this page is a little Animation of the concept: http://www.chemgapedia.de/vsengine/vlu/vsc/de/ch/26/igb/aquaponik/a...
Unfortunately this site exists only in german but here are some fotos of the system: http://www.eppenberger-media.ch/afrikanische-buntbarsche-lassen-tom...
Sounds great. Can you post some sketches of how the system would work?
In our research leading up to the design of our commercial system (300 square meters, flood-and drain gravel beds feeding medialess beds after that) we looked at all these fancy filter methods, but abandoned all of it. There is no aquaculture industry in South Africa, which means that all these nice things, as well as their spares, will have to be imported from overseas. Second, we want robustness, even if it compromises a little bit on yield. Where we want to build these tunnels, we would be the only back up. No suppliers or electricians or biologists for 100's of kilometers. We have great respect for a raised gravel bed with auto siphons in terms of aeration and filtration capacity. We have found other ways to optimise our systems, but not through the use of aquaculture-style filtration. Since fish value is not high at present, we can afford this outlook. Our financials work out on relatively little space for the fish, optimizing plant growth.