Backyard Aquaponics
A place to discuss aquaponics

Just wondering what a healthy ratio of Fish to Plants would be if i'm running a NFT system and the solid waste is not an issue. And im also growing lettuce.

It's more about surface area for nitrification than number of plants, though eventually you'll need sufficient plants to moderate nitrate levels. How many #s of fish (at maturity) are you planning on stocking?

I'm trying to figure out how many too stock, I know more than 200 based on my growbed volume I just need to know the ratio of nft lettuce.

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Any ideas anyone?

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Dagger,

As you've probably noticed, there is not much out there talking about stocking density for NFT systems... However one thing that might give you a rough idea would be to count holes in DWC systems that ARE well documented and compare that to the number of holes you'd have in your NFT system. As I recall when brainstorming about DWC design over on mwdesign's thread someone mentioned FAO recommended ratios of 1000L FT / 20kg fish / 4m² DWC raft. I think I've seen Dr. Leonard Wilson say 30 head of lettuce/m² of DWC raft. So if we can assume equal little quadrants for each lettuce, that'd be 1/30th of a square meter (0.033m²) which means about 18cm x 18cm for each little quadrant. So 4m² x 30 head/m² = 120 head of lettuce for the 4m² FAO ratios above. Of course you can spread out the DWC hole spacing a little because the plants on outer edges only have neighbors on 3 sides. Anyway, just assuming 18-20cm hole spacing for your NFT system, 5 holes/meter = 120 holes/24 meters. So...

1000L FT / 20kg fish / 24m NFT (at 20cm spacing)

So for your Fish / Lettuce ratio, say 500g fish / 3 head of lettuce?

How's that for a guess?

Actually I've read that NFT is slightly less efficient than DWC (whatever that means) so perhaps factor that down a little and consider the above guess at the high end of what you might be able to do.

--
Sam

So you have existing media beds and adding a NFT component and wondering what additional fish load you can introduce?

Exactly, I know that since the majority of the plant growth will be on the nft I should somehow be accounting for that in the fish population.

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Give yourself more credit than a guess
I'd call that an educated guess, It does seem like a reasonable number I'll take your advice and look at someone else's DWC system like you did thank you


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The difference between nft and dwc is the in nft you are not able to account for the sides and top of the pipes that are not under water. For instance the dwc's walls and the bottom of the styrofoam floats all give addes square footage for bacteria to call home. If it is a true nft, there is very little surface area that the water actually touches.

I didn't think that surface area for bacteria would be a problem if it goes through a growbed and a sump with added bioballs, I thought it was if theres enough plants to remove the nutrient build up.

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So if i have 1536, heads of lettuce on my NFT system and I also have 115.2 ft3 volume of growbed that means that
115.2*7.5= 864 Gal/ 5 = 173 fish + 1536/ 3 = 688 fish

So technically I should be able to raise about 690 fish. Do you guys think my math is correct?