I want to create a small scale aquaponics system this summer- I'm still in the researching stage of this project. Here's what I have so far- any feedback will be appreciated.
General Specs:
2X 200L (black industrial barrel) fish tanks (300-350L filled with water altogether)
2X 200-500GPH pumpwith speed adjustment (best quality pump I can find on Ebay) to transfer the water to
2X 100L Gravel grow bedssituated below the reservoir. 20mm (3/4inch) gravel that I can find in a nearby riverbed. Gonna introduce earthworms in the mix after the system is in the process of cycling (gonna add a few plants, and cycle using seaweed extract)
1X 100L Floating Raft NFT grow bed situated below the gravel grow beds (the gravel grow beds will act as the bio filtration and sediment removal. Container slightly wider on top than bottom, so that the styrofoam raft with the plants will lower when water level in the NFT container drops, but only for a few inches, which after when the water level lowers further, the roots will be exposed to air.
*The water from the NFT grow bed will empty into the fish tank.*
2X 50-100GPH Timer pump (plus speed adjustment), a plastic divider and
2X 100L container for the duckweed growbed/automated duckweed feeder.
?X PVC Pipes with plastic taps to transport water and regulate its flow (and to make Bell siphon).
2X Water heater
10X All Male Vegetarian Tilapia. 5 in each tank. Duckweed is going to be the main diet, supplemented with vegetable scraps. I don't plan on harvesting the fish, and I want to give them a decent quality of life- which is why the low stocking ratios. I planned on raising goldfish, but they don't seem to be very hardy.
I plan on growing pennywort, lettuce, and chives on my NFT system (main emphasis on the Pennywort- killer ramen garnish), and tomatoes, eggplants, and some other stuff on the gravel growbeds.
Lighting Plants will be lit either by regular fluorescent tubes, or nifty DIY Red and Blue LED growlamps (saves a lot on electricity- dunno if the plants need the whole spectrum- I read a few reports stating that Red and Blue are the only colors in the spectrum required for plant growth and production of fruit- your thoughts?)

In short, this system will probably have a 500-550L capacity- which is said to not be very stable. But this system is going to be predominantly indoors- either in an unheated sun room in the summer, and the basement in the winter, thus addressing the temperature issue. Unstable pH however, may become a big problem.
Your thoughts?