AP System Design Concerns

[Jeff G.]

 

 

Greetings AP Community,

Let me begin by expressing my gratitude for the education and inspiration this community has provided me. A heart-felt thank you to all who have taken the time to share their knowledge and experience. I have found your content to be invaluable in the planning of my AP system. 

There are a few design concerns that I would like to submit to the online brain-trust here for some feedback:

• Fish Density and Nutrient Concentration: I have some experience in the design and building of Koi ponds, and this leads me to question the tank size/fish population ratio that is commonly used in AP systems. Simply put, the fish density seems extremely high to produce healthy fish. I understand the reasoning supporting this particular design choice is that a higher fish density produces higher levels of nutrient concentrations, which in turn support more productive plant growth. But couldn't this be achieved by simply allowing the waste/nutrients to accumulate in the system prior to the introduction of the plants? And if this was really an issue, wouldn't AP systems utilizing much larger volumes of water, like deep-water raft culture, be unproductive?
• Fish Stress and Nutritional Values: Raising fish in such confined spaces would seem likely to stress the fish unnaturally. Do I really want to eat a fish raised in such a confined space? Do I really want to eat a chicken that spent its whole life in a cage on a chicken farm? No. Besides the chronic hormonal disturbances that this confinement stress would cause, I would also have to question the nutritional value of the muscle tissue (meat) that resulted from a lack of physical activity in this space-restricted environment. Expanding the size of the fish tank several fold could reduce this confinement stress, as well as reduce the likelihood of losing your entire fish population during a mechanical failure of the water pump or air pump. This additional water volume would also serve to buffer water temperature and pH changes, as well as provide a nutrient reserve to extend plant growth into the colder winter season when the fish are less active.
• System Nutrient Spectrum: If system nutrient input=system nutrient output, isn't the harvest of an AP system really just fish feed "disguised" as a leafy greens, vegetables, or herbs? Granted, plants are more than capable of transforming available nutrients into more bioavailable and complex forms, but does commercial fish feed (and plant supplements) contain a sufficient nutrient spectrum to support viable plant and human physiology? It would seem that a diversification of system nutrient inputs would be desirable for all of the living components of the AP ecosystem, and especially for the higher level organisms. Perhaps one could utilize vermiculture and black soldier fly culture to harvest the diverse nutrients from local waste streams and introduce them into the AP system, but I'm not sure about the practicality of this approach, any feedback on this possibility would be appreciated.
• Open Loop -vs- Recirculated Designs: Given the proper design and resources (available water), it would seem that an open-flow AP system would have a few advantages over a recirculating AP system. 
  • A functional separation of the plant-sphere and fish-sphere would allow for organism-optimized environments and nutrient delivery. Factors such as pH, temperature, and nutrient spectrum could be adjusted to optimize nutrient uptake for the plants without affecting the fish. 
  • With a dedicated biofilter for the fish-sphere in operation at all times, planting and harvesting schedules would be much more flexible.
  • A bottom-drain fed vortex filter in the fish-sphere could effectively harvest nutrient-laden water for use in water efficient plant-culture systems such as flood & drain grow beds (recirculating with a separate sump), soil or soilless wicking beds/planters, or NFT systems (recirculating with mechanical filtration).
  • Fresh water is routinely introduced to the fish-sphere to replace the nutrient-laden water harvested from the vortex filter.

Most of my concerns can be boiled down to this: You are what you eat. And following in the footsteps of Joel Salatin of Polyface Farms, I want my family to consume organisms that are healthy and happy:) As I lack any real experience in aquaponics, I defer to this community for an assessment of these concerns. Thank you for your time and feedback.

 

All the best....Jeff

[Sylvia Bernstein]

Pretty funny about the KISS tattoo, Jeff.  Given the depth of your questions you are obviously a tinkerer and thinker, so I can see where that challenge comes from!

For the record I'm not happy with the commercial feed supplies that are out there either, and I'm working with a feed provider right now to see if I can change that.  Meanwhile it is what it is...but know that there is a ton of work being done all over the world on trying to get to a more sustainable fish feed.  I think we will be seeing big improvements very soon.

[Jeff G.]

Hi Sylvia, thanks again for the reply,

You're completely correct on keeping things simple. Sometimes, I think I need to tattoo K.I.S.S. on my forehead :)  I finally got a chance to read Dr. Lennard's interviews that EcoFilms posted, and his perspective seems to echo the advice that you and TCLynx have provided me here. I still have some reservations about the system nutrient input being predominately composed of commercial fish feed, but I will try to find simpler solutions for this problem.

All the best....Jeff

 

[Sylvia Bernstein]

Hi Jeff.  I'll try not to write a novel again, like I did last time, but you bring up such interesting questions...

 

I am actually seeing a contradiction in what you are trying to achieve, and what you plan to do.  In creating an ecosystem the best designer you can use is Nature herself.  I recommend you simplify as much as possible, all the while asking how does Nature handle this?

 

Rather than adding vermicompost to the grow beds, just add worms!  They will create the vermicompost for you within the context of the system.  No, you won't be able to process your household waste that way - you will need another composting system for that - but you will be creating an ecosystem.

 

Second, there is no reason to ever "flush" a well-balanced aquaponics bed.  There are systems in Australia that have been operating for close to 10 years without ever being "cleaned out" or "flushed".  That is a hydroponic problem, not an aquaponic one.  Because we aren't using mineral salts, there is no salt buildup (unless you are adding salts for some reason, but that is another topic).

 

Stand along aquaculture systems are certainly doable, but they aren't aquaponics!  Aquaponics is an integrated, recirculating eco-system where the fish produce food for the plants through bacteria and worm conversion, and the plants filter the water for the fish.  Period.

 

Municipal water is fine to use as long as you off-gas the chlorine ether through a filter, bubbling it out with an oxygenator, or just let it sit in an open tank for a couple days.  Muni water is what most of us use.

 

Hope this helps, Jeff.

 

Sylvia

[Jeff G.]

Thank you Sylvia and TCLynx for the excellent replies, I really appreciate your effort to help me with these concerns, and you really clarified a few issues for me. 

I guess what I'm aiming for is a design that would allow for a greater diversification of organisms and nutrients in the "ecosystem". Integrating insect, worm, chicken, and rabbit cultures into the system would definitely complicate the design and require much more work on my part. But it would also allow for the harvesting of nutrients from household, garden, and community waste streams, which is something that I feel would be important for the long term sustainability of the system. 

I see no obvious way to achieve this integrated design without, ironically, segregating the plant culture from the aquaculture. I really like the flood & drain media bed design (utilizing the bell-siphon) because of its ability to provide excellent gas exchange in the rhizosphere. I think this gas exchange contributes significantly to the excellent plant growth seen in this type of AP system. But I want to be able to add vermicompost and compost (solids and/or teas) into the planting substrate without worrying about how these additions might affect the fish. In addition, I want to be able to periodically flush the plant-culture beds to remove toxins (or unused nutrients/minerals) that build-up over time. I don't see how I can add this operational flexibility with a traditional recirculating AP design. Perhaps I'm mistaken, can you offer any feedback on this?

I'm confident I can design and build a stand-alone aquaculture system with its own dedicated biological and mechanical filtration systems, as I have some Koi pond experience. Typically Koi ponds require periodic (partial) water changes to control nitrate concentrations and I know a few pond owners who apply this "waste" water to their gardens with fantastic results. Including a small raft-culture for lettuce and edible greens distal to the mechanical and biological filtration system might help to control nitrate levels during the periods between water changes/harvests. 

But the success of this open-flow design depends on one thing; available clean water. Obviously municipal water is out of the question without treatment, but what about rainwater collection and well water? I've read some pros and cons about each, but what does your experience show? 

Thanks again for your time and expertise....Jeff

[TCLynx]

1)  This sounds much like the dilution question.  Having more water in a system doesn't "dilute" the nutrients once things get cycled up and balanced.  However, you must make sure your water circulation and filtration can handle the larger water body.  Certain ratios tend to work for different methods of system and if you get too far off from these numbers there is a tendency to have trouble getting it all balanced nicely.  (For instance the situations where some one wants to turn the swimming pool into the fish tank and only use a small pump and grow bed because they only intend to stock a few fish, hard to get it balanced and cycled since a small grow bed can't really take the flow of the complete swimming pool each hour and a little pump won't do it so water gets turgid and full of algae.)

 

Still on number 1) Once a system is cycled and balanced, dilution is not a problem hence why raft systems work.  It isn't so much about the total water in the system but the balance between feed input and fish mass in relation to the filtration and the plant uptake.  Many of the "rules of thumb" are not only taking into account the fish to plant numbers but also making sure there is enough aeration/circulation for the fish and well as enough bio-filtration.

 

2)I don't like super crowded fish.  However, I have also learned that while I would never stock 1 fish per gallon for grow out, it also doesn't work very well to put just three catfish into a 600 gallon tank.  Too few of certain kinds of fish actually seems to cause more stress due to aggression and territorial behavior but if brought up to a higher density the fish will display more social/schooling behavior and the stress seems to be minimized until you reach a level at which dissolved oxygen and water quality become difficult to keep optimal and it is at that point where the stress starts climbing again.  For media based systems super heavy stocking is not required.  I've had fine luck stocking about 1 fish per ten gallons of fish tank and I have twice as much gravel bed volume as I have fish tank.  This still allows me to get 30 catfish in a 300 gallon fish tank and that number of fish seems to keep the territorial behavior at bay and still allow for plenty of nutrients for my deep grow beds.  Water quality stays good and the fish are not stressed.  When I have put ten catfish into a 100 gallon tank, they were stressed.  It is easy to tell when catfish get stressed, they get sick and white patches of skin are easy to see.

 

3) Fish feed.  As Sylvia says a high quality feed is essentially to heavy veggie production in an aquaponics system.  If one wants to experiment with alternative natural feeds, they will be experimenting and possibly struggling to create their own balanced feed.  The fish feed question actually is the most troublesome question to me actually because I'm not all that happy feeding my fish (and thus myself) food that is to a large extent, corn/soy and fish meal.  I'm definitely not happy about the GMO corn and soy as part of my diet nor that of my animals (I have chickens and ducks too as well as the fish) but I've not figured out how to feed my catfish well without it yet.  And the fish meal has it's drawbacks too.  Like perhaps not being sustainably harvested and the worry about mercury build up from it.  So improving the quality and sustainability of the fish feed is an important topic of aquaponics.  Some of the manufacturers are listening too and hopefully we will get some improvement there soon.  Currently there is not single magic bullet way to naturally feed your fish in an aquaponics set up.  Green water doesn't work well for aquaponics if you also wish to grow veggies and one way or another something needs to provide the balanced nutrients.

 

4) I agree with Sylvia here, simple works for me.  Perhaps you could get some improvement for certain little details by controlling every little bit but the amount of extra work, monitoring, waste of water and additional components needed to make the fish and plant systems separate doesn't seem like it really would pay off long term.  Then again, I tend to travel a week at a time and my systems need to look after themselves with only the neighbor wandering past once a day to collect eggs, make sure the pumps are running and top up feeders if empty.  I can't expect the neighbor to clean filters, transfer water or do water changes or test the water to decide when changes are needed or any other chemical type thing.  Now that might be reasonable in a commercial operation but definitely not for a backyard set up.

 

This should all be fun and simple once it's up and running.  I have experienced over stocked systems or systems that were not cycled up yet when a large amount of fish arrived.  I know what stressed out catfish and tilapia look like and I don't like that.  I too want my food to be happy and healthy and work hard to make sure my fish can express their natural fishness in good clean water.  I will continue to research ways to feed my fish so I can reduce my dependence on the commercial fish feeds or perhaps I will find feeds that address the primary concerns in ways I can approve.

[Sylvia Bernstein]

Hi Jeff. Thank you for your very thoughtful set of questions. You bring up a lot of interesting points here. I hope many people respond, but I'll put my questions and 2 cents in to start the ball rolling

1) When you are talking in the first bullet about stocking density, which are you referring to? Growing Power suggests a 1:1 gallons of water to lbs of fish, Nelson and Pade and UVI go to 2-3:1, the Rules of Thumb here, Murray Hallam, myself, and many members (most?) in this community shoot more for a 5 - 7:1.

2) What size tank are you considering to be "too small"? To a certain extent this is tied to the stocking density question above. Also depends on the species. Gold fish do great in a 20 gallon tank, right? Tilapia, and other fish raised in aquaculture are schooling fish and seem to be more comfortable when they are somewhat crowded. I think there needs to be some realistic considerations taken into account because the nature of raising live animals generally has some space constraints...and I think there is some room between giving a chicken an acre of pasture land (not even Joel Salitan would do that) and giving a tilapia 500 gallons of tank. So what do you consider optimal? Big tanks (over 250 gallons) are generally considered more stable than smaller tanks, so bigger is generally better...up to the point where it no longer makes sense for your family. But know that there definitely is a ratio of fish to tank to grow beds in a well functioning aquaponics system (which I'm assuming is the ultimate goal here, right?) where you simply aren't producing enough nutrients to feed your plants.

3) you are right - a high quality fish feed is extremely important in creating a complete nutrient for your plants. The activity of the bacteria and the worms also contribute to that output. One of the most incredible benefits of aquaponics is that this is exactly what you need for a complete plant fertilizer...just like good compost is also a complete plant fertilizer. Could adding in BSF enhance this? Personally I doubt it, but BSF make great, sustainable fish feed that reduce other waste streams so that would be the reason I'd suggest using them.

4) My personal take on open loop vs closed loop is it sounds like a lot of work and more water used for very little benefit. A closed loop system works very well...why mess with it for only marginal potential benefits?  I tend to gravitate toward the elegance of simple solutions, especially ones that mimic natural systems.  Again, back to Joel Salatin, the beauty of his system of first grazing a patch of land with cattle, then having it picked over by chickens is that he is taking advantage of natural systems.  What you are suggesting here is the equivalent of giving the cows feed (not just letting them graze), collecting their waste and bringing it to the chickens. Can you optimize each component better then?  Perhaps...but is it really worth it? A media aquaponic system is mimicking a marsh wetland.  Once you get it in balance (i.e. establish a thriving bacteria colony) and add in some red worms you can sit back and let nature do the work for you.  I think that is a very beautiful thing indeed.

Just my initial thoughts, but I'm looking forward to what others have to say...