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I've seen a few discussions about small AP systems and why they wouldn't work.  How could one be designed that would work?

I'm thinking something like 3 gallons fish-tank.  For a 2:1:0.5 rule of thumb, the system would need 6 gallons of grow bed, 3 gallon fish tank, and up to 1.5lb of fish.  Basically, put a full grown 1.5lb plate ready fish into a 3 gallon tank and hook it up to a 28qt storage bin for a grow bed.  The image this brings to mind seems absurd.

I remember seeing an article about pond filters.  The premise was to compute the rate that ammonia is produced by the fish (based on how much they are fed), the ammonia that is consumed by the bio-filter, and the water retention time in the bio-filter.  The target is to make sure that the bio-filter can consume ammonia at a rate at least as great as the rate the fish produce it, and that the water is retained in the bio-filter long enough for the bacteria to do it's work.  Is this basically what is needed to design a suitable system?

Dave

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at this level of size you just might want to give up on the edible fish and use the system for veggies only... smaller fish would do better any ways...

there are a few designs around the web for small table top sized systems... they run on the same basic philosophy of the low density fish stock systems... they may not be able to support a high enough nutrient level for all fruiting plants, but if you're looking for an herb garden or leafy greens, it'll do the trick...

check out the stuff for low density systems... they run like you're basic fish tank with natural plants instead of mechanical filters... or like small ponds, just better set up to separate the fish from the growing vegetation. 

I have a small system of just a 25 gallon tank and 25 gallon grow bed ... two 5 inch goldfish provide more than enough nutrients for the plants and they don't even need a ton of filtration. My pump was out for 5 days with no power and the fish did great.

try something like this... 60 gallon fish tank, 25 gallon media bed. just enough to have a somewhat stable system... still not much food production.

 

What are some of the desktop systems?  I've been digging around the net file a bit and haven't found these. 

The paper I mentioned earlier is called "DIY Bio filter and Venturi Project" by Jim Prior in 2006.  It has a section that goes over the math, "Design considerations for a DIY bio-filter for your pond".  The caveat is that this is a design for small to large outdoor koi ponds.

Ammonia production is based on how much you feed the fish.  Each kilogram (2.2 lbs) of fish food results in about 37 grams of ammonia.

daily ammonia production = (37/1000) * fish food (g/day)

Flow rate is suggested to be fast enough to turn over the volume of the pond between 8 and 12 times a day.  About 1/3 to 1/2 of the pond every hour.

Filter size is chosen so that there is enough water retention to ensure biological activity occurs.  The recommendation is to retain water in the filter for at least 10 minutes.  In other words, if the grow bed is empty, it should take at least 10 minutes to for the pump to fill it when it is full of media.

filter retention time = filter size / pump rate

There is however another consideration.  The bacteria need a surface to grow on.  The grow bed must provide sufficient surface area in the grow media.  This depends on the Surface Are to Volume Ratio of the grow media.  Gravel is noted as having about 100 to 200 square meters per cubit meter (100-200 m2/m3).  Several other materials are given in the table (bio balls are 550:1).  This is called the specific surface area (SSA).

From the article, "Each square meter of biologically active surface can metabolize nearly one gram of ammonia per day."

ammonia consumption per day = media ssa * grow-bed-volume

Next step is to plug in some numbers and see what happens...

BTW, is there a biologist in the house?  I'm just guessing at all of this based on some articles I found.  It might be interesting to have an informed opinion.

wow, youve done some research, and thats good for the sake of understanding what your doing.

there is some much easier math to get the numbers your looking for...

gallons x .266 = sqare(cubic)ft of grow bed.       i.e.- 100 gallons =26.6 sft of grow beds(@ 12" deep). ...or around 25%     

so with a ten gallon fish tank you would have 2.5 sft of grow bed, and could stock 2-5 fish and get plants to grow.

here is a little one i built a while back, it grew basil just fine...

i have to ask, why do you want a desk top ap system? there is no need to prove ap works or that you can do it... it works and you can do it...  Go Large! you wont regret it.

Hi Rob.  That's a great setup you've got - it looks a lot like the one I built for growing basil through the winter (it's too cold outside to grow).  I might build a larger AP system in the front patio next summer.  For now, I need basil.

I'm not sure where your numbers come from though... The most common ratio is 2 gallons of grow bed to 1 gallon of fish tank to 0.5lb fish.  Commonly people note that the grow bed size determines fish capacity.  This is consistent with the pond figures.

It's great that you found that 2-5 fish grow well in your system.  Can you provide some numbers to help me out?

* How much did you feed the fish per day (oz/day) - or how many fish and how big where they (lbs or inches)

* Size of the grow bed and media type

* Size of the fish tank (seems like 10 gallons here)

* Flow rate (how many minutes it takes to fill the grow bed)

* How often did you siphon out water and replace it with new water?

I'm not too good at intuition.  I can't say I understand it until I've worked through some math, make a prediction, and see it working.

If it's not to personal a question - why aren't there any fish in the tank?  Or rather, how long did they live?

Rob Nash said:

gallons x .266 = sqare(cubic)ft of grow bed.       i.e.- 100 gallons =26.6 sft of grow beds(@ 12" deep). ...or around 25%     

so with a ten gallon fish tank you would have 2.5 sft of grow bed, and could stock 2-5 fish and get plants to grow.

Lets work some numbers.

I have a 26 gallon fish tank with one fish that is 5 inches long (tip of nose to end of tail - not including fin.)  I have a 28qt grow bed.  I'm using a fountain pump of undetermined size to pump water from the fish tank to the grow bed.

So, how much ammonia is that little guy producing?  I have no idea how much I'm feeding him; a bit.  I could look at the fish food container, get its size and divide it by the number of days it takes to finish it.  But I just purchased it and I'm not wanting to wait that long.  Alternatively, I'll guess at feeding based on fish size (mine is already a grown adult; stunted from being in a 10gallon tank most of his life).

I found this little link on feeding carp (goldfish / koi),

http://www.texaskoi.com/index2.php?option=com_content&do_pdf=1&...


At 6-7 inches, the fish should be about 0.15 lbs.  I'll be conservative and assume my fish is 0.15 lbs; close enough.  The tank is about 66F, so it suggests feeding at about 2%.  Google says that gives me 1.36 grams/day.

daily ammonia production = (37/1000) * fish food (g/day)

Or, daily ammonia production = 50.32 milligrams.  Lets just say 0.05 grams/day of ammonia.

I'm using lava rock for my grow media.  Google is my friend,

http://www.russellwatergardens.com/Styles/filtermediassa.php

Lava rock SSA is 86 SSA per cubic foot.  Converting to metric, Google gives me 282 m^2/m^3.

ammonia consumption per day = media ssa * grow-bed-volume


Converting 28qts to m^2 and multiplying against 282 m^2/m^3 and I get about 7.5m^2.  Each square meter gives 1g of ammonia consumption, or 7.5g/day.

The prediction is that my grow bed can handle ammonia production from 5.5 fish.  For 5 fish in my tank, they get about 5 gallons of water each.  That seems quite reasonable.

However, I still need to address retention time. 

filter retention time = filter size / pump rate

My pump fills the grow bed in about 5 minutes. This isn't good as my retention time is then 5 minutes before the water going in overflows back to the tank.  I need 10 minutes.  However, I run the pump for 30 minutes, then turn it off for 30 minutes as the water drains.  This gives 15min retention for the water sitting in the grow bed before it drains.

The grow bed is 28qts, but it's full of lava rock.  So, I measure the inside height of the tank at 16".  Then I marked the water line of the fish tank when the grow bed is full.  Let the water out of the grow bed and measure 2" of height gain.  So at (26 gallons / 16inches) * 2 inches, I get 3.25 gallons.  The pump is running at 3.25 gallons/5 minutes, or 39 gallons/hour.  Lets just call it 40 gallons per hour - sounds about right for a small fountain pump.

I need to make sure I cycle the full tank once every 2 or 3 hours.  I currently run the pump for 30 minutes, this moves 20 gallons of water.

I'm only retaining 3.25 gallons for 30 minutes as it drains.  This water happens once every hour.  It'll take about 8 hours to run through the 26 gallons tank, or about 3 times a day.

To get good ammonia consumption, I should probably add a valve to the water line to slow down the fill rate to 10 minutes.  This will filter 9.75 gallons in the 30 minute flood period.  All of the water in the tank is then cycled in 2.6 hours.

Auto-siphons drive me nuts though.  If I siphoned off all the water each 5 minutes, I would only get a retention time of 2.5 minutes.  There isn't near enough time for the bacteria to do its job.  I don't understand why auto-siphons work as well as they do at these high frequencies.  But if you use a 2:1 GB:FT ratio and cycle the FT water once an hour, then assuming the media takes up 50% of the GB volume, the siphon is only triggered about once an hour.  This provides plenty of time (30 minutes on average) to convert ammonia.

David,

I am (was) a fisheries and wildlife biologist with a minor in Aquaculture.  There are a lot of assumption made about aquaculture vs aquaponics.  I have been torn apart a few times on this site about making comparisons but what I will tell you from aquaculture.

Each speicies of fish is different.  All have a different rate of ammonia creation, water temp plays into part of this as well as diet and fish mobility, space to swim.  Food type, rate of feed also contribute to ammonia creation.  Aeration and DO (dissolved oxygen) are also needed to be considered.

If your not a fan of the KISS method 1:1 tank to bed ratio and the 1lb of fish per 10 gallons of water, and remembering what species you have, never assume a goldfish is done growing. Dr. Suess had a good book on that.  I have seen Comets live for 9-10 years in captivity and grow to 9+ inches.  Local nursery has a comet that is 18" long and weighs 4lbs, I would refer you the study of biometry, specifically Aquaculture Biometry, the math of biology

Agreed, John  -there are many variables to consider and it doesn't stop with the type of fish.  

Consider that If your system is one that encourages fish to swim rather than just slowly move around, this will effect the protein conversion to flesh of the fish and therefore the amount of waste produced in proportion.

If there isn't enough room or oxygen to support activity, then that has to be considered when calculating potential nutrient production.  


John Cubit said:

David,

I am (was) a fisheries and wildlife biologist with a minor in Aquaculture.  There are a lot of assumption made about aquaculture vs aquaponics.  I have been torn apart a few times on this site about making comparisons but what I will tell you from aquaculture.

Each speicies of fish is different.  All have a different rate of ammonia creation, water temp plays into part of this as well as diet and fish mobility, space to swim.  Food type, rate of feed also contribute to ammonia creation.  Aeration and DO (dissolved oxygen) are also needed to be considered.

If your not a fan of the KISS method 1:1 tank to bed ratio and the 1lb of fish per 10 gallons of water, and remembering what species you have, never assume a goldfish is done growing. Dr. Suess had a good book on that.  I have seen Comets live for 9-10 years in captivity and grow to 9+ inches.  Local nursery has a comet that is 18" long and weighs 4lbs, I would refer you the study of biometry, specifically Aquaculture Biometry, the math of biology

RE: "Filter size is chosen so that there is enough water retention to ensure biological activity occurs.  The recommendation is to retain water in the filter for at least 10 minutes.  In other words, if the grow bed is empty, it should take at least 10 minutes to for the pump to fill it when it is full of media."

Hey David, 

Where did you get this portion of your information?  Did you derive the last part yourself or was that part of the recommendation?

You want the flow through rate to be @10 minutes on settling filters to allow time for things to sink and some biofilters if there's adequate aeration within the biofilter chamber.  

Consider that when media beds are your biofilter, and it takes 10 minutes to flood, the lowest roots are underwater and may not be getting enough oxygen for a longer period of time.  If it takes also takes 10 minutes to drain, that's probably too long (in this case, 10 minutes is the maximum).  Roots will alter to compensate to a point, and it's not that the plants won't grow or even thrive, but the best conditions are made by an aerated quantity of water, a constantly flowing aerated water column, or a quick flood and drain.

I did many tests with hydro-organic systems in the past using biofilters.  At later stages in the trials, I actually started pitting ebb/flow, aeroponic, and NFT against each other.  I was able to achieve as good or better results in ebb/flow by using a bigger pump and larger drain fittings, and more frequent waterings... quick flood, quick drain, exchange nutrient levels more often.  The quick flood meant that nothing was under water for too long a time, and the quick drain drew air into the spaces that were previously filled with water.

Easiest thing to do would be to aerate the water as it comes into the grow bed (via venturi for example), or flood and drain faster.

David Palmer said:

What are some of the desktop systems?  I've been digging around the net file a bit and haven't found these. 

The paper I mentioned earlier is called "DIY Bio filter and Venturi Project" by Jim Prior in 2006.  It has a section that goes over the math, "Design considerations for a DIY bio-filter for your pond".  The caveat is that this is a design for small to large outdoor koi ponds.

Ammonia production is based on how much you feed the fish.  Each kilogram (2.2 lbs) of fish food results in about 37 grams of ammonia.

daily ammonia production = (37/1000) * fish food (g/day)

Flow rate is suggested to be fast enough to turn over the volume of the pond between 8 and 12 times a day.  About 1/3 to 1/2 of the pond every hour.

Filter size is chosen so that there is enough water retention to ensure biological activity occurs.  The recommendation is to retain water in the filter for at least 10 minutes.  In other words, if the grow bed is empty, it should take at least 10 minutes to for the pump to fill it when it is full of media.

filter retention time = filter size / pump rate

There is however another consideration.  The bacteria need a surface to grow on.  The grow bed must provide sufficient surface area in the grow media.  This depends on the Surface Are to Volume Ratio of the grow media.  Gravel is noted as having about 100 to 200 square meters per cubit meter (100-200 m2/m3).  Several other materials are given in the table (bio balls are 550:1).  This is called the specific surface area (SSA).

From the article, "Each square meter of biologically active surface can metabolize nearly one gram of ammonia per day."

ammonia consumption per day = media ssa * grow-bed-volume

Next step is to plug in some numbers and see what happens...

BTW, is there a biologist in the house?  I'm just guessing at all of this based on some articles I found.  It might be interesting to have an informed opinion.

David, i understand you like to do the math on things, but, you dont need to think about it that much.

the math i use accounts for the ratio you mentioned, it gives you the size bed to build... a gallon is .133 cft , times 2 is .266

all you need to know is how big of a media bed to build for your fish tank of choice, then how many fish to stock. then use a timer on a perforated stand pipe for a minimum of 15 mins/hr. ...this is all in the basic "Rules of Thumb" listed on this site.

-the picture above was when the system was first put together. the one 3/4 lb male tilapia lived in there for about 4 mos.  

 

 

 

John, it's wonderful to have your input on this!  As noted, I'm just a math guy with just enough information to be dangerous. 

Certainly each fish has it's own characteristics.  The idea is to work through the most important factors and provide guidance for smaller systems of 30 gallons or less.   This is not for producing fish to eat, but having pets that help grow basil.  Goldfish should not be recommended for this purpose as they can grow up to 12" in length.  Maybe small Chichlids would be good (http://en.wikipedia.org/wiki/Cichlid).  What other fish would be good?

I did some extra calculations and found a contradiction that suggests the math I'm doing won't work as stated. Something else is needed or the fish will die.

Lets consider the rule of thumb requiring 2 gallons GB to 1 gallon FT to 0.5lb of fish.  People providing this information aren't stupid - they know that if you exceed this rule of thumb, things are likely to go bad.  Meaning, fish will die.

Lets say that we have the worst possible media, smooth stone at 70:1 SSA.  For each gallon of grow bed, I get an ammonia consumption at 0.26 grams/day.

The highest feeding rate from my source document suggests 3% of the fish weight (farms want to fatten them up, maybe they provide more food than this?).  Thus for each 1lb of fish, we're feeding them 13.6 grams of food/day.  This then produces 0.5 grams/day of ammonia.

So, how many fish can the grow bed bio-filter support?  I'm coming up with 0.75lbs per 1 gallon of grow bed.  That's a bit much.  Especially when you consider that the recommended density is 0.5lbs per fish tank gallon.  In other words, we're stocking at 1.5lbs of fish per every 1 gallon of fish tank!  What a breakthrough! 

Clearly something is wrong with my assumptions.  From what I've read, aquaculture farmers spends a lot of time removing fish solids from their tanks.  The cited source on the bio-filter even notes that a pre-filter is required for the bio-filter.  This pre-filter is needed to remove fish solids.  Without removing them, we have another waste input that isn't being address, thus leading to fish deaths.

What can be done about fish solid waste?  1) use a siphon to remove it every week, or 2) grow worms.  Certainly the siphon is what aquariums normally use as the bio filters for pet fish don't process solids.  You can get special under-gravel filters so that you can remove the solids.  I really hate doing this.  But if the solids aren't removed, then I expect the fish will die.

The second option is to add worms.  Not any old worm, but composting worms - like red worms or tiger worms.  I just went to my compost pile and dug some up.  I don't use manure in the compost pile, so it should be clean of e-coli.

But another equation is needed here.  How much solids do the fish produce?  How quickly can worms consume the solids?  What is the maximum worm-holding capacity for a given container?  I don't know... do you have a reference to an article to aide in my education?

I have two options of where to put the worms: I can put them in the pea gravel at the bottom of the fish tank or in the grow bed.  Goldfish like to dig.  I suspect he'll find the worms if they are in the pea gravel.  However, in the grow bed, the worms would have plenty of room.  They will reproduce until the worm population is able to consume all of the fish solid waste. But then I need to remove the pea gravel and replace it with sand.  This is to make sure the solids don't get trapped in the gravel and can get sucked up by the pump and delivered to the grow bed.

Hopefully the guy with his kids school experiment drops in.  I could run some numbers to see what kind of setup is more likely to survive if my assumptions aren't too far off the mark. 

Do you have a small AP setup?  Please post the details so I can check to see if this meets with the theory.

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