Backyard Aquaponics
A place to discuss aquaponics

Right now I am comparing and contrasting the advantages/disadvantages of NFT vs DWC, NFT seems to have an advantage in oxygen seeing as the roots are not entirely submerged allowing them access to atmospheric oxygen not just devolved oxygen, thus plants like tomatoes can do well while in DWC they struggle (or so I have been told) but this advantage has nothing to do with the thin film of water only the gap between the net pot and the water, could suspending the "rafts" of a DWC system a few inches over the water provide the same advantage? The reason I ask is the downside of using NFT with large fruiting plants, the blockage that the aggressive roots can create, while the high volume of a DWC system would easily accommodate such root systems.
Looking at ways to grow tomatoes and peppers without having to pump huge volumes of water through raised ebb and flow beds.

Just pump more air into your DWC rather than suspend the boards above the water if you are concerned about their oxygen levels. It's not worth the trouble, trust me. I have tried what you are saying (sort of) and it was a miserable failure for the most part. I have grown tomatoes in a DWC and they thrived. Most productive tomatoes I have ever grown.

I always wondered if the Kratky method of hydroponics could be applied to DWC aquaponics where over time you slowly lower the depth of water in your DWC beds creating airspace for roots. Here are details on the Kratky method:

http://www.ctahr.hawaii.edu/hawaii/downloads/three_non-circulating_hydroponic_methods_for_growing_lettuce.pdf

The problem I see with it, is that all the plants need to be around the same age.

That's fine for the large farms, but I like to stagger growth, and want a continual crop of lettuce, and the new pots wouldn't be touching the water, while the older ones are thriving.

If using foam as the raft and it is thick enough then you could cut the holes on an able to leave an air gap around the roots.. made easier by planting in those hydro plastic pots perhaps?

The edges would break off tom.

perhaps but they don't have to go to a complete point like that… also something I have been thinking of using instead of the usual foam is a boat floatation foam that is closed cell and practically indestructible which comes in about 50mm thickness.. although I would want to check if it is safe to use chemically, especially since it is fire resistant.

Maybe you could add additional strips of foam to your raft between plants raising the raft thereby increasing the amount of air space. Then you could solve Columnmn's problem of staggering production by using different rafts for crops of different ages. This would allow you to leave the H2O level the same.

Thanks for in input yall, I think the way I would space them on a plant as heavy as tomato vines would be to skip the foam all together and suspend a stronger wooden (sealed of course) plywood structure on the edges of the DWC tank and use a threaded stand pipe drain to control the water level/ air gap. I would think anything over 3" would be dancing with the point of diminishing returns.

The thing I'm curious about. The roots that are exposed to air, don't they just turn into stems/harden up without the constant moisture? While you'll still need to aerate the 99% of the root system that's still full submerged?

I understand that in flood and drain type beds, the air is added when the GB drains, but in a DWC bed the majority of the roots would be fully submerged in the water, even if the top inch is raised. And I'd have thought they'd still need aeration to avoid stunted growth.

Don't plants take up all the oxygen/nutrients/nitrogen through water? I'd have thought if the roots are raised out of the water, they can't take up the oxygen?

Thinking kind of along the lines Tom did. You could make lifters for the net pots so they don't sit all the way down in the hole. Wedges might be an easy way to do this. Might get more algae this way unless you block the light though.

I ran about an air gap under my raft and the bottom of the net cups were just off the top of the water. The turbulance and popping bubbles created by the air stones makes everything wet under there and the media wicks as per normal. Pretty simple really.

I read in a PDF on Hydroponics that there was a benefit to having this air gap between the nutrient solution and the bottom of the floats,hydroponics don’t generally aerate there nutrient in the DWCs so this air gap encourages Air Roots which improved the growth rates within the plants.
In AP where everything is in competion for the available DO, i took the route no air gap,high turnover and lots of air,Ryan of Chattersons Farm actually helped me with the minimum amount of air i should be using.
Charlie has the best of both and his growth rates atone to that,air gap and moist air from the addition of air stones,there could be the point that maybe you don’t need as much air as when you float the raft.

Google bubbler buckets; they rely on as Charlie said an air gap and an extremely moist atmosphere with droplets of nutrient being popped into the gap by the bubbles bursting.
Reputedly very good for growing tomatoes in your wardrobe.

How about a raft that is porous enough to let air roots through but block light.