Calculating water in NFT

[Hollis Armstrong]

Ok I know and understand square footage of the media beds, its an easy calculation if you have 4 x 8 x 1 ft bed then you have 32 sq ft. When you calculate fish/sq ft ratio its usually 1 lb/sq ft of media grow bed.

 

My question is how do you do the same type of calculation for NFT pipe beds. If you have lets say 100 ft of 4" pipe with 2" holes for the 2" net pots how do you calculate that to find out how many fish you need?

 

Just trying to get my fish to grow bed calculation correct.

 

Thank you

 

Hollis

[Hollis Armstrong]

Also does anyone know how to calculate how many ft of NFT pipe beds you can have for any given amount of media grow beds?

Since the media grow beds are the bio filters for the fish water before you can run it through the NFT pipes, how many feet of NFT pipe can you have for each square foot of media grow beds?

So if you have lets say a 1000 sq ft of media grow beds then how many ft of NFT pipe (4") can you expect to receive that water and still have enough nutrients to feed your plants?

[Vlad Jovanovic]

That will figure will depend more on the amount of input feed going into the system and what plants you have in those media beds...

You may find that you need additional filtration between the beds and the NFT to operate them successfully and consistently in the mid to long term.

Another consideration to ask yourself is "since the NFT channels act as a heat sink in the summer, how long can my NFT channels be before the water warms up too much, thereby depleting itself of enough oxygen to be able to grow plants"...and the accompanying problems that occur with such anoxic, warm water conditions (pythium, root rot, crown rot etc)...

The reverse is of course true in the winter...NFT channels then act as a cold sink...so if heated water is coming in at one end...at the other end it comes out at a temperature about equal to whatever the ambient air temp is. Is the profit garnered from sales of the NFT vegetables enough to justify the extra cost of electricity (or whatever energy input) that it now takes to heat that water before it goes back to the fish tank (or while it's in the FT)?

NFT channels are GREAT when temps are mild...like in the Springtime, or in the Fall (unless you're lucky and happen to live somewhere where it's mild all the time

You may consider DWC troughs which actually add to the thermal stability of a given system through sheer water volume the add to a system. They (DWC troughs) can also be easily insulated during construction with extruded polystyrene sheets...

Remember, large volumes of water are a great thermal mass, the larger the more thermally stable...as opposed to thin films of water moving across a (relatively speaking) massive surface area...which will QUICKLY pick up or lose heat from that surface (in this case a PVC channel).

[Hollis Armstrong]

hhhhmmmmm Interesting information Vlad. Deep water may be better. Then again perhaps the grow towers would be even better as I understand that they also act as a bio filter like that of the media beds. I'm just not as versed in the towers yet. I may have to revisit that and try to understand them better. I have read where some people (someone whos opinion I respect) said that they had lots of trouble with the DWC. 

I'm assuming that lettuce is going to be a large portion of my business and so Im looking at how to best fit that product into the system to maximize the space. 

Im now looking at 42 x 96 greenhouses as they are less expensive as the 30 x 120''s. and they give more sq ft space per house. My current thought is to have 40 (4 x 8 ) media grow beds to grow various produce per house and the rest of the space I wanted to dedicate to lettuces of various varieties. I like the idea of the net pots for speed in collecting mature lettuce plants and replacing with a seedling. 

[Vlad Jovanovic]

Not sure what kind of trouble they were having...or why...but DWC is one of the easiest, oldest, most well suited for commercial scale production of water culture greens and lettuce on the planet.(Both AP and hydro)...

For "speed" and labor net pots kinda suck actually. In the first large-ish AP system I built I have 1,286 holes in the 8" on center production rafts (plus 648 in the nursery trough)...it's a time consuming pain in the ass to reclaim all that hydroton and all those net pots. In subsequent systems I use 1" plugs...and have been meaning to try some of Rob Torcellini's GrowGrips instead of the net pots in the original system since the GrowGrips (like net pots) are re-usable...

Re-usability is the upside to the net pots, but the plugs are much, MUCH "speedier"...

These are pictures of that system utilizing the 2" net pots...

  Pictured below is a system I built for a client whose rafts use the 1" plugs...

 Again, I don't know what type of trouble your friend was having, or what the cause of the trouble is...but many, many people are using the DWC successfully...

[Hollis Armstrong]

I have looked at the plugs and I must say that is something to look into. I see you are growing well while there is snow on the ground outside. How hard is it to keep your greenhouse heated, especially enough to keep the fish happy? Want to share what heat you are using? The plants look awesome. Way to go Vlad