Appropriate Water Depth in Nutrient Flow System?

[Bill Moore]

I assembled the 4 inch PVC pipe nutrient flow system to supplement my grow bed.  After a bit of tweaking of the plumbing, I've got it flowing properly, but should have asked what is the appropriate depth of water in this system?  Right now the depth averages just over 2 inches, with the outflow point at 2.5 inches. Is this too high?  It's about 1 inch into the bottom of the planting cup with peat liner.

Here's photo of it under construction.  1 inch outflow pipe now redirected down into the fish tank.

[Francois Lemmer]

i think +-25 mm between roots and water works ok

neat work

[TCLynx]

NFT actually means Nutrient Film Technique and in the original idea you would only have a thin film of nutrient flowing through the bottom of a flat trough.

However many people run something more like a shallow water culture where the water in the pipe is 1/2" to 2" in the pipes and the main thing is you want to make sure the water stays well aerated and doesn't block up with roots and overflow so the main thing about depth for such a set up is, are your plants able to reach the water?  I use wicks so I don't need to worry about the net pots getting water logged or dried out.

[Bill Moore]

I'll get the nomenclature right someday.  :-)   NFT....   Mine is more like Nutrient River Technique!  

I've got 5 test plants going, so let's see how they do.  I think there should be plenty of oxygen in the water.

Bill

[Chris Smith]

My flat bottom NFT channels use about 1/8 to 1/4 of an inch of water in the bottom. The roots do great because they get lots of Oxygen.

It looks like you are pumping out of your fish tank and into your NFT before your gravel bed. It is best ue use the gravel bed as a prefilter to keep poo off the roots of plants in the NFT. Without proper filtration roots in NFT can accumulate organic material and turn anaerobic.

[TCLynx]

Oh, you are right Chris.  I didn't really look at the picture.

Yea plants in a pipe getting un-filtered fish water tend to have issues and it good get stinky after several weeks.  I definitely prefer to use water after it comes out of the grow bed to feed NFT pipes though that might be tricky to do in that set up.

[Vlad Jovanovic]

What would be a good slope to use (1 in 30, 1 in 75 etc...) if using 110mm (4") pvc pipe? I have some unused real-estate  on the north wall of the greenhouse near the sump that would lend itself well to some NFT add-ons. Would flow rates of about 1 liter per minute still sound good with such a set up (non-flat bottom gullies and deep water, deep meaning an inch or two)? 

[Bill Moore]

Water for NFT is coming from sump.  Sump is feed from grow bed and from fish tank, which has nylon filter to trap particulates.  

bill

Chris Smith said:

My flat bottom NFT channels use about 1/8 to 1/4 of an inch of water in the bottom. The roots do great because they get lots of Oxygen.

It looks like you are pumping out of your fish tank and into your NFT before your gravel bed. It is best ue use the gravel bed as a prefilter to keep poo off the roots of plants in the NFT. Without proper filtration roots in NFT can accumulate organic material and turn anaerobic.

[TCLynx]

ah, ok, I thought the tank in the picture was the fish tank and that the NFT was fed by it.  You might just find that you need to add some extra filter material between your fish tank and the sump tank to help catch most of the solids so they don't gunk up the roots in the pipes.

[Bill Moore]

Since the system is in a fishless cycle, the water is pretty clean. There is a filter over the outlet of the 2 inch pipe into the sump to catch any solids.  I'll clean this periodically.  Also half of the water filters through the grow bed.  My chief concern is that I don't 'drown' the plants  The 2 " deep water is hardly a 'film,' but I think the water is getting plenty of oxygen from the way it gushes and bubbles when the siphon drains into the sump.   Time will tell.  I am prepared to do a bit of re-engineering to to get it right.

[TCLynx]

You may find that you want less water in the pipes but just keep a close eye on things so you know if/when you need to do modifications.