NFT flow rates

[Jon Cavin]

There have been many discussions with regards to height of water in the channels, pitch, flow rates, etc.  I am wondering if anyone has any different success stories, including length of tubes, number of plants per tube and ofcourse the importance of aeration.  I am currently using a 1/4 hp pump going up 6 ft feeding 9 individul tubes.  My flow rates seem good to me but I am basing that on virtually nothing.  My water depth in the tubes is approximately 1/4" maybe a little more.  The tubes are pitched at around only 10 degrees.  Any additional experience would be welcome. Thanks.

[TCLynx]

I've only got two 15 foot lengths of NFT pipes. Mine are actually round pipes and not proper NFT channels. I don't have much pitch in mine and I'm sure there is usually between 1/2" and 1/4" of water in the bottom. I don't add extra aeration to my pipes but the water in my sump tank that the pump draws from is well aerated and it is growbed filtered water so fairly clean.

[Nate Storey]

Hi Jon,
I've done a bit of NFT in previous aquaponics systems and have had good luck with them. I've used flat bottomed PVC gutter and inclined it at around 5 degrees pitch. (most commercial hydro NFT systems run at 5 degrees or less- many around 2 or 3 degrees. it shouldn't matter too much though). You can do troughs as long as you want, but I've found 10' or less most conventient. I've just used sticky velcro tape to tape them to my table so that I can move them around and remove them for cleaning. I clipped them in at the top with some clips/tubing brackets that i hotmolded from scrap PVC. I inclined my tables with turnbuckles on the high end (hinged on the low end). I covered them originally with hard covers, but then just switched to black visqueen film duct taped to the sides of the troughs. They were gravity fed from a gravity feed tank about 11 feet off the ground but ran around 3 gpm. you don't need to aerate your troughs if your flow is moving at a reasonable rate (3gph or more, not too fast, not too slow), shallower is better so long as your pump doesn't fail, and gives you more surface area to volume, which means your gas exchange will be better and you'll have higher O2 content in your water. Your roots will trap plenty of solids, and if your water is shallow and has good air exchange this isn't always a bad thing. . . just keep an eye on it, hose it out every now and then and make sure you're smelling it to make sure you don't have any anaerobic issues. I think 1/4 inch of water is a good depth for flat bottomed stuff, but if your using tubes, then it'll have to be deeper.

[TCLynx]

Nates instruction to make sure your smelling it is an important one!!!!!!

A comment about NFT and solids. When I first hooked up a bit of NFT pipe, I was feeding it water directly from the fish tank. The system was fairly heavily stocked. It did not take very long before the solids were clumping up around the plant roots and the smell was able to make me gag.

The very small suspended solid particles don't seem to be a big problem in my current NFT pipe situation (the kind of solids that tend to get through a filter or a grow bed) but the larger slimy glop that will come out of a heavily stocked fish tank with no additional filtration can become too nasty and anaerobic fast. In that initial set up, it would have meant pulling the plants and washing their roots and blowing out the pipe ever 3 or 4 days which would probably set the plants back too much and be too much work to make it worth it.