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I understand the difference between NFT & DWC but my question is how deep is the water in each system?      I want to build one or the other after  the growbeds  but I want if to be gravity flow so I need an elevation shift between it and the GB.  Also which would be better? I dont plan on using except to only grow lettuce when weather permits. Thanks in advance.L F

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Hi LF,

NFT channels have a thin film of water at the base. Net pots touch the water and the media in them draws the water up and to the plant roots. DWC have a minimum of 12 inches of water and net pots touch the surface water also drawing water to the roots. NFT channels heat up easily with sunlight and causes lettuce to bolt early. Of course you can shade them to help to keep temps down. DWC has more water volume and won't heat up as readily and grow lettuce quickly and easily. Its good that you're placing these after the GB to provide filtration and clean water to them as roots clog with fish waste and the plants suffer as a result. 

DWC usually also has supplemental aeration added to it and can be as simple as a frame or block on the ground with pond liner that the grow beds drain into it.
Thanks alot for the answers. This brings up another question. how does NFT & DWC calucate to your FT? In other words I still have room for 320 sq.ft. of GB so how much NFT orDWC do I need ? I understand the ratio between fish and GB, and working the math with numbers leaving room to add fish later with experence.  Thanks again for sharing your expertise.

Hi LF,

These ratios are mostly found through the actual experience of growing crop yourself. There are many variables but i think it depends mostly on the feed regime. Some say 1/3 lbs fish per square foot of DWC. I personally have used 1 lb of fish to 6-8 lettuce in both NFT and DWC and get a zero ammonia/nitrite reading in the standard 24 hour period. If you do try a specific ratio, and are getting readings above zero after 24 hours you need to increase your plant ratio or decrease your feeding, which ever is more appealing to you.

The numbers for a low density system DWC might look like: 4 gallons of FT per # of fish, 1/3 # of fish per square foot of raft space, and 1.5 cfm aeration per 100 # of fish.
WOW dont take many fish to grow lettuce. No wonder they try to tell you you can get rich.

Hi LF,

You have to keep in mind that your GB's are going to pre-filter waste going to the NFT/DWC. The GB/Fish ratio in the ROT document is designed to accommodate pounds of fish to cubic inches of GB. If we add plants loads by incorporating DWC or NFT as attachments to the GB, we will have to supply more nutrient(Fish Feed), this in turn will generate more waste, and depending on the plant volume, will result in the GB's becoming overwhelmed and develop clogging/anaerobic issues.If the additions are large, independent filtration will become necessary. In my experience you can get away with about 30 percent plant load  over the ROT and avoid the clogging issues.  

Thanks Harold  I was aware of part of this this is why I was using the smaller numbers. I dont want to over load anything until I think I know what Im doing. Im digging my FT under my GBs and wont be able to change them after I set my GBs up. after I get all the dirt work done I intend to put a greenhouse over the whole mess. Maybe I'll have fresh vegetables when no one else does.

Hi LF,

Best of luck, posting some pics as you go along would be nice

don't go making things too hard to access.  Make sure you don't have to depend on the fish coming to a particular part of the tank for inspection.

 

And there are many factors involved in finding the right balance for an aquaponics system.  You may find you can grow even more plants per fish depending on the fish feed and water chemistry of your particular situation or if you get cheaper fish feed, you might need to use more to get the same plant growth result.

Thanks TC    Im planning on making my FT about  2x3x50 with an open area every 16ft. By putting them under th GBs I'll have more space for GBs. Of course there will be more GBs for this size FT. Thanks again. LF

TCLynx said:

don't go making things too hard to access.  Make sure you don't have to depend on the fish coming to a particular part of the tank for inspection.

 

And there are many factors involved in finding the right balance for an aquaponics system.  You may find you can grow even more plants per fish depending on the fish feed and water chemistry of your particular situation or if you get cheaper fish feed, you might need to use more to get the same plant growth result.

How will you keep the fish from hiding under the grow beds when you go to harvest?  Will you have to get in the fish tank and walk down it with fish gates to corral them into the accessible areas?  Even in a completely accessible tank, it can be really challenging to harvest fish, some fish are more challenging than others.

 

Also make sure you can see all parts of the fish tank from your access points so you can easily inspect for dead fish and have long handled nets so you can remove dead fish should you need to.  Having to go snorkling with a flashlight (don't laugh, I know of a system where that is required) in your fish tank to inspect/remove dead fish is really not the most favorable way to deal with it.

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