Backyard Aquaponics
A place to discuss aquaponics

hi, i am trying to build a commercial AP system on the roof of my house.
the grow area will be vertical nft mainly (4000 holes total) each plant 20cm apart
i will grow only small leafy greens such as lettuce and herbs.

i will write my calculations below so please review them and advice as you see fit.

1)

if nft was a grow bed my m^2 would me 4000/25=160
where 4000 is the total plants and i have read that you can grow 25 lettuces in 1 m^2

according to the UVI i would need 60-100g/1m^2/day and lettuce is not a heavy feeder so i will go with 60g/m^2/day
also according to the UVI in NFT systems i need 25% of that feed ratio so 70*25%=15g/m^2/day

so for 365 days and 160 m^2 i need 15*160*365=876000 g/year or 876 kg/year

2)
also according to UVI the feed to fish connvertion ratio is 1,7 lets say for tilapia
so with 876kg of feed i will grow 876/1,7= 515,29 kg of fish growth
if i aim for 500g per fish i will have 1030 fish i will now take into consideration the starting fingerling mass for simplicity.

3) those fish will be grown in 26 weeks so i will have to house half the above fish mass at any given tine and the fish production will be staggered
so 515,29/2=257,65kg of fish

4) according to the UVI the fish stocking density is 0,5 pounds/gallon as a pound is 0,45 kg and a gallon is 3,79 lt(approximately) the above fish density is 0,5*0,45/3,79=0,059 lets say 0,06

so for 257,65 kg of fish i need 257,65/0,06=4294lt of fish tanks






my main concern is the weight of all this water because i don't want to burden the building with 4500 kg



so i am asking what can i do to grow the most amount of plants with the least amount of fish

thank you for your time in advance.

Adding a mineralization tank would help. A lot of UVI's solids were removed from the system instead of being completely mineralized. You could grow fewer fish and add nutrients and solids (if additional nutrients were needed) to be broken down, into the mineralizer. Once processed they could be fed into the system.

You might also be able to split the system into the plant portion and the fish portion with the fish somewhere that the weight won't be an issue and a much smaller sump tank to run the plant portion.

>> so i am asking what can i do to grow the most amount of plants with the least amount of fish

that would generally require some level of supplementing.
Depends quite a bit on the plants you want to grow beyond the lettuces.

AP without fish and with supplements is hydroponics - guess the question is what do you want of the fish ?? At a commercial/large size hydroponics or something similar would probably be more efficient. For larger plants you could go dutch/bato buckets (but that is probably not not relevant to your case).

At smaller scales / home production then you could probably go down a wicking bed type path.
But that does not sound practical for your case.

4500 kg is not a lot of water (4,500 litres or 4.5 IBC's).
I cant see your fish load being very big to operate at a commercial scale - is that just fish tank or is that water in the tubes/beds as well ? there is a big difference between one 4000 L tank (or two 2000L tanks) versus 4 IBC's for example when it comes to fish and stocking levels.

Hi Perklis, I just read your post and agree with 1 2 and 3 and then got a little confused on 4. Did I misunderstand or are you saying you will start with 572 fish at 450g each. If that is correct then 572 fish in 4294 litres is only 7.5 litres per fish Before they start to grow.......

Disclaimer...... As my name implies I'm no expert but this seems awfully high density to me.

Again only having limited experience and relying on others on YouTube I came to the conclusion that 450g of fish need between 19 and 37 litres per fish! Depending on whether you want high or low end density.

If that was true then 572 fish (450g each) at 19litres per fish would be 10.868 litres before they grow.

Maybe im totally wrong (it's been known) (often) but please clarify no 4 again. Good luck. KE

3) those fish will be grown in 26 weeks so i will have to house half the above fish mass at any given tine and the fish production will be staggered
so 515,29/2=257,65kg of fish

4) according to the UVI the fish stocking density is 0,5 pounds/gallon as a pound is 0,45 kg and a gallon is 3,79 lt(approximately) the above fish density is 0,5*0,45/3,79=0,059 lets say 0,06

so for 257,65 kg of fish i need 257,65/0,06=4294lt of fish tanks



i will start with 257.65x2= 515 fish (fingerlings) so i end up with 515x0.5kg of fish= 257.65 kg of harvested fish per cycle of production... 6 months each cycle

Ok now I understand thanks for explaining. I just got confused.

I did manage to find this on the aquaponics source...... Not my words! Just copied and pasted......

They start by saying...Today’s DWC aquaponics systems evolved from the good work of Dr. James Rakocy and his team at the University of the Virgin Islands (UVI). then go on to say... DWC systems with solid waste removal equipment can generally handle up to one pound of fish for every two to three gallons of water IF they are designed properly and well maintained.

That's for DWC... Further down in the article they talk about systems with media beds.... A media based system, on the other hand, requires no external solids filtration. Instead, the solid waste is sent straight into the grow beds where it is mineralized (broken down into a form that is available to the plants, thereby adding to the food available to the plants) by heterotrophic bacteria and composting worms. Because this is a natural, balanced system versus a more human-intensive system; stocking density recommendations tend to be a more conservative one pound of fish for every five to ten gallons of water.

That's the only reason I said it sounded a little high density. I hope you get it sorted out. Good luck with your system. KE

>> i will start with 257.65x2= 515 fish (fingerlings) so i end up with 515x0.5kg of fish= 257.65 kg of harvested fish per cycle of production... 6 months each cycle

the real question is how you will run this. Yes you can start with 515 fingerlings.... but 4000L is not a lot of water.
Will it be 1 x 4000L, 2 x 2000 or 4x 4000L. Will it be 1000L as 0.6m deep circular tank for a 1000L IBC. Many of the commercial systems are incorporating pretty high levels of water management and filtering along with fish husbandry (ie. basically more like aquaculture systems).

Without experience it will be hard to carry a maximum stocking rate to full course...
most people start conservative and build up to optimum levels over time.

Unless you know what your doing you would be advised at running at .25lb per gallon and even at that level you and your equipment needs to be up to speck,the UVI were seasoned professionals who knew how to run at those high stocking levels,at .5lb per gallon your almost on the threshold of need O2 injection,so if anything goes even slightly wrong it could spell disaster.
As someone starting out I would even advise to start lower than .25lb until you slightly more experience.