Aquaponics Cherokee national forest 

I am staying in the Appalachian mountains at an aquaponics farm for 2 months. Here is what I learned:

  • How it works:
  1. You have fish tanks with fish eating food that you give them
  2. The fish poo in their water
  3. The poo water gets drained to the ‘sump’ tank at the bottom
  4. This water is then pumped in to the growing beds (big tanks filled with stones)
  5. The water is continuously filling to the top of the grow beds, then when it reaches a few inches from the top of the gravel it automatically drains out (it’s now been purified by the stones and roots)
  6. Pure water is pumped back to the sump tank then the fish tanks to start again

  

The grow beds 

  • Limestone can’t be used, granite gravel is good, sand is being experimented with 
  • Clean all dirt off rocks before starting
  • Red wiggler worm are added to the stone beds and they clean the lettuce roots
  • It was really labour intensive planting the seedlings in the gravel. Digging a hole in the stones was painstaking work, especially when compared to planting in soil which takes seconds per plant. I feel using sand would overcome this problem  
  • You have rocks etc in your grow beds which need to become coated in bacteria. The bacteria convert the nitrates into nitrogen? So that it can be used by the plants. You have to run your system a few times before the bacteria grow to suitable levels so rocks you have had for years are going to work much better, however I think you can start with lettuce as it doesn’t need much nutrients and can grow without the bacteria to begin with 

Nutrients and plants 

  • You can grow all year round
  • You can use compost using a ‘tea bag’ system. You have an extra pump and a bucket of compost. You pump the water into the compost which is in the mesh bag in the plastic bucket. This gets the nutrients in to the water. Drain the water in to the sump tank and let it flow round again. The compost may need to be heat treated though as it can kill the fish if it contains bacteria 
  • You need to monitor plants to check for deficiencies of certain minerals, which you can then add chemically
  • New system you need to check water pH and other levels, the older the system and better established the bacteria are the less you need to check
  • A standard aquaponics set up can only grow nutrient-low food like herbs, tomatoes and lettuce. This is because of the lack of nutrient-rich soil, so I guess you can grow more if you add the nutrients to the water through soil or artificially maybe
  • During very hot months it isn’t possible to grow lettuce
  • First grow the seedlings till they have good roots, a few weeks maybe, then transfer to the grow beds

Structure 

  • You can’t have see through pipes (to check for blocks) as they would form algae
  • An efficient way to cool the green house if it gets too hot would be to have a vent at the top and bottom. This would take advantage of the convention current and quickly cool the greenhouse 
  • Create as little shade as possible with the structure (thin beams, few as possible)
  • Paint outside of plant tanks to stop sunlight getting through and creating algae. Can paint silver to keep all light out but this would reflect heat in winter and you might need that. Dark green is good.
  • One sump tank needed per 4 grow beds of equal footprint
  • LED lights work fine so you can create a solar powered indoor tower system
  • The greenhouse climate control must be on thermostats. Therefore you can only grow products with a similar temperature range in each house. 
  • For climate control you need: 
  • A vent at one end which opens when for example the temperature reaches 20 degrees 
  • At the opposite end a fan. The fan must be set to switch on just after the vent, so maybe at 25 degrees. 
  • Then you will probably need a heater for nights, which will set to switch on when temperature drops below a certain point, say 15 degrees. 
  • Looking at the Eden project, they use a dome structure with ETFE windows. Making it wind resistant, and light. Could a dome be the most efficient shape (not considering land use) 
  • Here is my research in to their structure: 

  

Fish

  • With a large enough system you dont need to keep all the waters seperate. So for example you can pump fish poo water as well as clean water into the sump tank, these can mix and then be sent straight back up to the fish. This doesn’t work with smaller systems. The bigger the system the less you need to maintain and check in this respect
  •  One fish tank can produce enough poo to supply 5 grow beds with the same size footprint
  • One system per crop type. So greens can all grow in one row and whatever crops use the same nutrients can be used in the same row 
  • Better to have clear fish tanks to see when you have dead fish 
  • To increase nitrites, feed the fish more
  • If you want to grow the fish to sell you need to have a filter to filter the poo before it gets to the grow beds. This is because you will have more fish in the tanks than you need to fertilise the plants.
  • A pH increase could be caused by ammonia from a dead fish

Example income tomato bed (2metre high cherry tomato plants)

  • 1 square metre 
  • 10+ plants 
  • 40+ tomatoes per plant 
  • 400 tomatoes per bed 
  • 3 months per harvest 
  • 133 tomatoes per month per bed 
  • Tomato weight 0.02kg
  • Weight per bed per month 2.66kg
  • Weight per bed per harvest 8kg
  • Weight per square metre per year 32kg  
  • Average supermarket sale price £2.50 per kg
  • Farmers market income £80 p/sq.m p/yr (bed only)
  • Total income 15 beds £1200p/yr
  • Total greenhouse footprint 10x7m. 70sqm
  • Including walkways, fish and sump tanks £30 p/sq.m p/yr
  • 1 hectare. 100x100m. 10,000sqm can make £300,000 p/a

Example lettuce 

  • £20 p/sqm p/month
  • £240 p/sqm p/a
  • 1 hectare grow space (considering walkways) is 4725sqm
  • £1,134,000 retail
  • -70% wholesale = £340,200 income 

Business model 

  1. First Greenhouse GH1: grow lettuce, establish bacteria, fast returns (crop every 40 days)
  2. Greenhouse 2: once bacteria established in GH1 (after a year maybe), move lettuce to GH2, grow herbs in GH1
  3. Greenhouse 3: move lettuce to GH3, herbs to GH2 and start tomatoes in GH1. 
  4. Keep moving crops till you have reached the desired variety. 
  5. Maintain the following order:
  6. Newest system – lettuce 
  7. Second newest – herbs 
  8. Third newest – tomato
  9. Fourth and more – move to higher and higher nutrient crops 


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