Backyard Aquaponics
A place to discuss aquaponics

I'm looking to build a compact patio set up, with the goal of moving to a more permanent indoor location and expanding in the next 12 to 18 months.

Proposed hardware:
1 50 gal/ 90 liter fish "pond" (I have this)
2 48" tall by 4" media-filled grow towers (built from PVC, est. volume 5 gal/ 19 L each)
1 cubic foot ebb and flow bed with bell siphon (7 gal/ 28 L)
1 6" to 8" square DWC raft (scrap styrofoam, mostly to improve fish habitat)
1 agromax250 pump and lots of plastic irrigation tubing (I have this)
No sump or additional filtration

Biological and other inputs:
Not more than 2.5 lbs/1.2 kilo "feeder" goldfish total
Fish feed will be duckweed, mosquito larvae, and fish flakes
Towers should hold 16 plants each, DWC 1 or 2, all salad greens and herbs
Plants will get additional compost tea foliar feed 1-2 times a week.
I add city water, allowed to stand for 12 to 24 hours to off-gas.
I will use a combination of gravel and scavenged styrofoam peanuts for media

Configuration:
The single pump will power the system. Beds will be plumbed in parallel to maximize flow-through rate, and will drain directly back to the pond. Water in excess of what the beds need will cascade directly back to the pond to help with aeration.

Stats:
I need to add 2-3 gallons of water weekly to my present 40 gallon bottom-watering system, so I'm expecting a roughly 5% weekly water change here, too.
Rough ratio is 1 lb fish: 20 gal H2O: 6.8 gal grow bed

Questions:
I have two 5" long gold fish. I have ready access to 2" long fish. How many more do I add to reach my desired stocking rate this season?
Are my calculations correct?
Given styrofoam media, how much water should I anticipate running through the towers per hour? How much through a gravel-filled EFB? Will these actually provide enough surface area and flow-through rate for adequate biological/mechanical filtration?
Are the ratios feasible? Because the system is small and I have little experience, I want a large margin of error to protect the fish. I'm worried that these ratios won't support plant growth, even with foliar feeding.

..50Gallon.. is that not more like 200L

Bottom line, there are techniques by which you can have LOTS of fish and LITTLE grow media.. BIOCENOSIS
..

I'm more interested in doing amoderate amount of plants and little fish. Winter plant loss is expected, but the fish at this point are pets, not food. I find that with my little above-ground pool I need to move the fish to smaller indoor containers 3 to 4 months out of the year. I'll double check my conversion numbers; thanks for catching that.