Backyard Aquaponics
A place to discuss aquaponics

Yep!... ST, not FT... typo, sorry.

As far as ratios for NFT and DWC are concerned, I've never run either in my aquaponic systems. I prefer to simply run 300mm deep gravel GB's and plant a variety of plants, including the small leafy greens that many do in NFT/DWC, such as Lettuce, Asian greens etc. The 300mm deep gravel gives a good ratio of fish (nutrients) per square metre of GB surface area for the healthy growth of most vegetables... Tomatoes excepted.

I have a number of customers that have had systems like that described above running very successfully and then they've decided to tack an NFT or DWC component onto the system, invariably they run into nutrient deficiency issues within a very short period of time... because they haven't increased their safe fish stocking capacity (nutrients) but they've increased the square meterage of their GB and therefore the amount of plants.

To overcome this we've played around with different gravel depths/stocking rates in ratio to area of NFT/DWC components and come up with a rule-of-thumb that works in most backyard situations where only small leafy greens such as Lettuce, Asian greens, herbs etc are grown in the NFT/DWC component.

I've found that if a 400mm gravel depth is run in the gravel GB's and extra fish stocked in ratio to this extra 100mm of gravel, then an NFT/DWC component with an area of between 50% to 100% of the gravel GB surface area can be sustained... 50% for a mixture of greens or all hungrier greens such as Asian Greens, Coriander, Spinach etc... and up to 100% ratio if running Lettuce only.

I hope that explanation is not too confusing.

What I did was make my GBS deep so they had more volume but less planting area and then added DWC to make up the extra planting area that had been reduced by making the GBS deep.

So if you use the 1:2 ratio 300 mm deep GBs as your bench mark Then if you double the depth to 60 mm deep GBs then you want as much growing area again in your DWC as in your GBs.
If you triple the depth then you want twice as much growing area in your DWC as in your GBs.