Backyard Aquaponics
A place to discuss aquaponics

I think it would be better to gear NFT area to the water volume, the depth of the film and the level of available nutrients.
As an example, a 200L barrel of gravel will provide biofiltration for 50L of water and a given weight of fish pro-rata. If you spread the 50L of water into a film 3mm deep (NFT) it will cover an area of almost 180 sqft.

For comparison, a flood and drain gravel growbed 300mm deep would have an area of about 7 sqft. Assuming the pump cycle is 15 on, 45 off, you will have a thin film of water on the gravel for 75% of the time. Discounting the solids, the film is largely responsible for the bulk of the growth.
Every sq mm of gravel surface in the bed not directly utilised by a root is effectively wasted as far as plant growth is concerned as it is covered with exactly the same nutrient rich film.

If you have sufficient bio and solids filtration in the system, the limiting factor for plant area in nft (and any other system) will be the nutrient level available

here are two links to free unit converters I frequently use:
unit converter:
http://www.rjhsoftware.com/unitconverter/
omnicon:
http://members.execulink.com/~pjones/

they are a great help

Frank

Have no trouble with your postulation that removing "solids" decreases the "potential" bio-filtration requirement of a system Frank....

But to go on to say ...



Is stretching things a bit Frank....

Firstly, increasing your bio-filtration via growbeds... hence converting ammonia/nitrites to usable nitrates for plant growth is the whole purpose of growbeds...

More growbed capacity, more bio-filtration... and as TCL said... if used at the 300mm depth as opposed to "deeper"... then more surface area available for plant number/growth and nitrate uptake...

Your original postulation of solids removal was in relation to removing nutrient load in order to maintain higher stocking densities...

Here we're concerned with maximising plant growth/nutrient uptake in a given amount of space...

Removing part of the nutrient load/solids... via whatwever means, including water changes... just seems counter-productive if we're trying to maximise plant volume...

If not, and fish mass is important, then, yep as I said... run it like a recirc system with solids removal...

Secondly though Frank... there is a scarcity of literature regarding any "harmful" or "stress" related affect to fish stock from nitrates...

The only info around suggests that it may possibly occur at levels of at least 400+ - 1000.... over a sustained period of time...

And the literature conceeds that such water quality parameters have only ever been artifically created and maintained for very short periods of time....

It just doesn't normally happen.... a natural balance is always acheived, one way or another... even if by pond/plankton crash.... total water quality parameter upheaval... etc...

In which case the fish aren't stressed.... they're dead.... but not from the nitrates as such... but by other water quality parameters, usually DO....

Members (JP in particular) have run extended high nitrate levels in AP systems ... albeit, not by design...

Generally, most solve it .... by adding more growbeds and growing more plants.... bonus...

Don't forget, regardless of growbed media, nft, floating raft etc... plants will only take up what nutrient intake they need... regardless of available volume... as long as sufficient...

Different plants have differing needs in terms of both nutrient uptake... and nutrient composition...

NFT can be limiting in this regard... usually to green leafy vegetables... ie lettuce, basil, asian greens...

Flowering/fruiting plants require higher levels of Potassium and Iron, in particular.... and can even be defeicient in these elements if the growbed with solids scenario as traditionally used is employed....

To go strip solids out... to then add trace elements back in at a later stage to do NFT ...

And to dump water... just seems contrary to what the holisitc nature of AP is at it's core...

Might just as well do a straight hydroponics operation and have more control over it....

yep.

I read this post at 3 am this morning , and thought thank god someone has spelled it out to me loud and clear on the directon I should be taking with stage two and three in my yard. I think I am going to put in a " home made " hyroponics system, that used to be in use by an old bushy up here, before Cyclone Vance levelled part of our coast. Its a nutrient tank that was sunk into the ground, and the guys NFT channels are guttering incorperating the black plastic over it. I am just going to set it up how he had it set up and give it a shot. Then add on a second aquaponics system with the flood and drain cycles, making my own tank, and bigger.

you are misquoting me twice, Rupert
The first time by overlooking the word "depth"
the second time by omitting my comment on dumping water

reread my post and you will agree

frank

Quoted - reread my post and you will agree

frank

or u will be shot

Greetings Hygicell, Rupid made the MOST sense to me about the situation of aquaponic and then diverting to a NFT then back again system. Thankyou ROZ. Simplistic aquaponics is the key, and as TCLynx has stated several times, aquaponics and flood and drain are vital in an aquaponics system, for the bio filteration and any other diversion is a

Didn't misquote you at all Frank.... quoted you EXACTLY as you wrote it....

Just went on to suggest that, while utilising growbeds of greater "depth" certainly added bio-filtration capacity...

And accepting that the greater depth (in it's self) didn't result in nitrate removal...

Both, as you so rightly suggested....in fact the extra nitrification would actually add more nitrates ....

But RATHER that utilising shallower growbeds with greater surface area... allowed for more numbers of plants... that would utilise, hence reduce, the nitrates....

Removing the bulk of them from the system.... without the need to "solve this by water exchange" or "by letting go contaminated water to drain" ....

The essence and wonderous simplicity of Aquaponics.....

please not another yes/no discussion

the subject of this thread is pushing the numbers of fish, not trying to maximize plant volume
we should keep that in mind

TCL suggested to double growbed depth
I replied saying that that would increase biofilter surface but not remove the nitrates which will build up.
Whether that is harmful to the fish or not is indeed not proven, so I wrote it might be, not it is.
And there is a telltale that such a build up is harmful: why else would intensive aquaculture recur to daily partial water changes?

so if you would want to push the numbers of fish and avoid nitrates build up you would at a certain moment be forced to dump water
a conclusion that TCL also had reached since TC suggested to carry some water to your house plants
(I was not suggesting to dump water, quite the contrary: I clearly stated: we don't want that, do we?)

If you want to increase fish density and still want a balanced system you have little choice but to increase both biofilter surface to convert nitrites to nitrates AND plant growing surface to consume the nutrients.
So increasing only depth is not a good enough solution, you must create more surface too.

Unless...
Unless you remove some nutrients from the system which is fairly easy to do (without needing to dump any water).
ans still stays respecting the holistic nature of AP at it's core if you use these nutrients to produce fish food (worms and duckweed) and compost (worms).

This is what I wrote
All you wrote is true too, so we don't really contradict each other
But the subject of the thread is pushing the numbers of fish
I kept that in mind

greetings

Frank

Also, keep in mind that nitrogen is not the only nutrient that is dumped into the system by feeding the fish. There is even less information on the effect of these nutrients on fish. High nitrate levels go with high levels of other nutrients, and I don't think that fish would like that for extended periods of time (even though in some cases it worked in AP).
I agree with Frank that in those cases frequent water changes are best for the fish - though it'd be better to add more growbeds, or like Frank suggested, remove the nutrients in another way.



Healingdeva, I ran those numbers (1700l FT, 3,25 sqm GB) through my calculator and it says:

Minimum for optimal plant growth:
95g of fish food a day (enough to feed about 12 big 500g fish).
Maximum the GB can handle:
380g of fish food a day (enough to feed about 50 big 500g fish).

This is assuming an average fish food protein content of 35%, a fully planted diverse growbed with good solids filtration and a pump of 930 L/h or more at growbed head.

If you feed less than the minimum, you won't get the best plant growth, and if you feed more than the maximum then you will have excess nutrient buildup.
As small fish don't eat as much as big fish, you will probably have less nutrients in your system than your plants would like, if you start out with only fingerlings. You could try to find some big carp (I got mine for free because they don't have beautiful colours like those Japanese ones) or other big fish that eat a lot to start up the system while the fingerlings get bigger. I suggest about 20-25 fingerlings and a couple of bigger fish to start out with.


By the way, my system has only slightly more FT volume, and less GB area (2,7 sqm) than yours. I'm keeping 35 or so fish (lots of different sizes and species); they're not for consumption but they're growing well and getting really big. It seems a bit crowded in my pond, even though I'm still feeding slightly less than the calculated minimum at the moment. Next year the fish will be big enough to feed them more though.

How bout this. A double depth grow bed will provide extra bio/solids filter and provide a good amount of space for plants. Since it is double depth, it will be able to filter for more plants that It can support directly so this might be a good option if there are ways to add vertical growing space like towers or some NFT troughs is space that might not be acceptable for grow beds but something up out of the way might be ok and thus take care of the extra nutrient load.

There, best of both worlds. You get the flood and drain filtration plus the use of the extra nutrients without haveing to haul water to houseplants or fish poop to the worm bins.

right
that is why all my horizontal piping consists of NFT channels
and when my fish grow bigger and I have to feed them more, or when I harvested my growbeds, I can tap off some of the nutrients to feed to the worms or the duckweed to feed to the fish
win win win

frank

Wow, thanks Xzorby! Now, the mathematician in me wants to know how you came to all of that.