Aquaponics system Design in W North Carolina

[Sunil Patel]

Hello everyone, I'd like to thank you all for all the info I've gleaned from all the discussion threads here.  It's much appreciated!

 

        I am taking over an existing aquaponics greenhouse system in western north carolina.  The system was established last year and has the following features.

42 ft3 of bed volume

1500 gallon tank (200 ft3) in greenhouse

small outdoor pond integration possible (as a sump tank possibly or backup water supply)

 

        It seems like a big imbalance to have the bed volume (42 ft3) so much smaller than the tank volume (200ft3).  If the system was run with this setup, the fish waste would constantly be diluted, and the plants would not grow well.  I'm hoping to get feedback on this conclusion I've come to.

 

       Here are my goals for the system and the strategies I'll use to help them along.  I would love if some of you could poke some holes in this plan.

 

Goals:

1. focus on high short term veggie yields and long term fish yields (1-2 years till harvest).

2. make system 4 season

3. make system a closed loop between fish and plants to maintain high control over production and water quality.

4. work towards making infrastructure strong, long-lasting, and able to handle the highest potential of the system. i.e, growbed:tank and pump

5. make system financially viable (minimize inputs and labor costs).

 

         To meet the goal of designing for the highest potential of the system, I have come up with the following maximum design scheme.

grow 185 lbs of fish

1% feed rate @ 45% protein

273 ft3 of growbed

1500 gph pump (total head of system taken into account)

 

        [Lennard's calculator gives a flow rate of 559 gph.  I am trying to reconcile this with widespread information on cycling the entire tank volume every hour.  does it mean the bed requires that flow rate in order to process the water?]

 

         for this season, in order to maximize short-term vegetables yields I am thinking of adding 140-160 ft3 of growbed.  This would give 182-202 ft3 of total growbed.  When the growbed volume is maximized based on space in the greenhouse, I'll come up with the final figure for the fish poundage and feed rate.

 

          In order to make the system 4-season, with minimum energy input,  the fish species needs to be chosen carefully (hybrid bass is where people settled at the end of last season, still need to know more what temps are they hardy to?).  And the crop plan needs to continue through the winter to keep the biofilter going.  Data collection while it's cold out will be key, and water heaters may or may not need to be kept on backup in case of deep freezes.  Feed rate should go down in winter if temps are cold, and cycling can slow down.  grow beds will be designed to allow for second layer of protection for the plants so winter green can continue to grow.  Plumbing should be insulated if exposed to cold and low flow rates.

 

           In order to keep control over the system, I would rather the fish/plant system is kept separate from the small outdoor pond becuase the pond has all kinds of life in it, and so, many unknown variables.  I'm not sure if this is a valid concern or not.

 

           Soldier fly larva production, duckweed production, and other feed production techniques will be employed fully.  BSF will be the priority.  5 gallon bucket BSF larva harvesting systems will be employed.  Duckweed  will be planted in outdoor pond.  Aim is to minimize purchased feed as much as possible.

 

           Right now I'm thinking of stocking the tank with bluegill or some similar coldhardy fish that reproduces a lot.  And then introduce predator cold hardy fish like hybrid bass when bluegill breeding is ramping up, and see where the evolution of the multispecies system should go from there.

 

Would love some feedback on my thought process here.   Thanks!

[Jon Parr]

How large is your GH? You certainly have done your homework, good for you. That being said, not all guidelines are gospels, especially the one about pumping 1 FT volume per hour. That kind of flow would be difficult to even get to move through your GB media (or are you using DWC?) I've seen excellent results from a GH that had 2600 tilapia in 5000 gallons, and 4000 square ft of DWC, using only 1800 gph.

I think it is wise to add GB as soon as possible, but having a larger FT than necessary is ok, and doesn't mean that your nutrients will be diluted. You should stock according to your planted area, not your FT. A good guideline for stocking is a MAX density of 1 pound of fish per cubic foot of media (which is the same as square ft of growing area, if your beds are a foot deep). That means you max out at 42 lbs of fish. If you're considering a fish load of 185 lbs, your water will be anything but diluted. Oatmeal is probably a better term. Anyway, I know that the 185 was an eventual figure after adding beds, but my point is that you won't have nutrient deficiency if you stock and feed according to your GB, regardless of your FT volume.

Bluegill will readily breed in the tank if conditions are appropriate, but keeping enough zooplankton alive to support fry needs is another story. You are better off letting them breed in the detached pond, and trapping some fingerlings to stock the FT growout.

Good luck, and I look forward to watching your progress.

J

[Sunil Patel]

Thanks Jon, 

Yeah, I found some local experts who told me what you told me just now.  It's good to know dilution will not be an issue.  

The design project for the system has taken a couple wild turns, should be interesting.

 I didn't mention we have a large pond up the hill from the greenhouse.  Right now it has a huge clutch of frog eggs, and lots more life happening up there.  Instead of trying to fit GBs in the GH, I'm leaning towards doing a system where the upper pond is stocked with more fish (working towards bluegill hybrid bass polycultures).  The water then gravity feeds through a series of filters (vortex, or radial flow filter -> bead filter -> degasser)  Then into a raft system in the GH along with the growbeds in there.  Prob, no fish in there.  Then the water would be sent down to another little pond to be cleaned even further and back up to the upper pond.  

Still working through the design process.  Will keep you updated!