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Just Don

How many fish?

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Okay... I've seen various "rules of thumb" out there for designing an aquaponics system (i.e. 1:1 ratio of volume of grow beds to volume of fish tank). However, I'm struggling with how I can know how many fish my system can support. How can I calculate the "carrying capacity" of my system knowing that I have built it to a 1:1 ratio.

Obviously the chemistry is different between systems that have the right volume ratio if one system has a single fingerling and a grow bed full of plants, and the other has 100 full sized fish and one little seedling. (I suspect in the first case you'd have scrawny "weakling" plants, and in the second case you would soon have much fewer than 100 fish.)

Any suggestions? (My intent is to have a grow bed full of seedlings planted at 6-8" intervals, and to stock the FT with tilapia fingerlings.)

Thanks,

Don

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Actually the best ratio is 2:1 that is twice as many grow-beds to the volume of your fish tank, but usually everyone says 1:1 as a starting point. Most people plan for fish at there harvest weight regardless of the size when they put them in the tank as a rule of thumb. I remember someone saying 2.5 per fish if that helps..

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one thing it would be good to know is what grow bed media you have used and what volume of it you have. From here people who are brighter than me will be able to calculate the surface area provided by your grow bed. That lets us know how much space there is for bacteria. From there we can calcualte how much waste they can process, this is normally a weight of food. Then from that we can calculate the weight of fully grown fish you can support, at a feeding rate of x% of their body weight per day.

I'll leave some one else to do the calculations as i can't say i'm 100% sure on them my self.

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Actually the best ratio is 2:1 that is twice as many grow-beds to the volume of your fish tank, but usually everyone says 1:1 as a starting point. Most people plan for fish at there harvest weight regardless of the size when they put them in the tank as a rule of thumb. I remember someone saying 2.5 per fish if that helps..

2.5 what per fish? Gallons? Liters? Something else?

Thanks,

Don

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one thing it would be good to know is what grow bed media you have used and what volume of it you have. From here people who are brighter than me will be able to calculate the surface area provided by your grow bed. That lets us know how much space there is for bacteria. From there we can calcualte how much waste they can process, this is normally a weight of food. Then from that we can calculate the weight of fully grown fish you can support, at a feeding rate of x% of their body weight per day.

I have roughly 30 gallons of grow bed media, which is about 75% red lava rock (bottom of GB) and 25% river rock (top of GB).

Thanks,

Don

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The variables are to many to be able to get a ratio like that, every system is a custom design, every place water comes in contact, bio film well be created and then bacteria will forum. As everyone's system is a custom design and there seems to be no set standard to building a system, one person use one kind of media another uses something else, then the size and depth of grow beds are a little different in each system. the length of pipe is different, one person used more pipe the next uses less pipe.. It just goes on and on.

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Sorry that would be 2.5 gallons per fish.. but fish density really depends on your DO you could have more fish if there is enough DO to keep them alive. I have seen 1 fish to a gallon before.

Edited by Pugo (see edit history)

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Don,

I've sat here for 20 min typing up the calculations i have done for my bio filter working off your grow bed size and potential biological surface area, and i'm afraid i just can't provide a calculation as i don't know how much more efficient media in a bio filter is than the media in your grow beds. So i'm going to have to step back from giving you an answer.

What i have done for my system is assumed that the growbeds will do nothing, and all my calculations are based on my bio filter which means my growbeds are just a safety buffer for the system. I'm running 50litres of K1 media in my bio filter and that supports 250g of feed per day, at 1% feed rate that is 25kg of fish that i can support at harvest weight, assuming i want to harvest at 500g thats 50 fish. In all honesty though i will start lower for safety as things like oxygen levels will become more of an issue than what food i can process.

***Steps aside to let some one with the right answer come forward***

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there are many different answers, but what helped me the most was a basic rule for bio-load..

for every 100 gallons of growbed, you can grow out 25lbs of fish (final size).. another formula bases it on sq/ft of growbed, but does includ the volume and "roughly" works out the same if you're growbeds are 1' deep

people have a tendency to push boundries, and have found ways to increase the load (additional filtration, additional oxygen etc)

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About the only thing you can get a ratio on is K1, everything else will be guess work even I based my system off of my MBF. As far as fish density, even though I know my brush filter acts as a bio filter to and so does my grow-beds.. But I have never found a ratio that would work to many variables.

You also need to take in account the green leaf area of your growbeds as they remove nitrates from the water. Which is huge factor you have to think about.

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K1 (kaldness media) is a filtration media that is "neutrally bouyant" that some people use to make a floating bed biofilter..

as long as you don't overstock, gravel growbeds provide plenty of filtration

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Start at density 14 metric or 30 US. Feed rate 1%. You can then lower your fish density if your grow bed (leafy greens) is too large to make the grow bed fit your fish tank size.

http://www.aquaponic.com.au/backyard.htm

Then fill out form below.

To get a total number of fish you'll need the projected Average Fish Weight.

I wanted to know the same thing.

Fish biomass calculator.

http://www.aquaponicshq.com/forums/showthread.php/6093-Fish-Biomass-Calculator

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Start at density 14 metric or 30 US. Feed rate 1%. You can then lower your fish density if your grow bed (leafy greens) is too large to make the grow bed fit your fish tank size.

http://www.aquaponic.com.au/backyard.htm

Looks like mostly Tom Losordos work without credit....

From what I can see that calculator, which has been found incorrect once, the latest version is far from accurate.

So let's take a look....

[ATTACH=CONFIG]2905[/ATTACH]

This first one has 1000 liter tank with 20kg of fish. the surface area of the media used is 1. Changing that only changes the size of the bio filter results which you see in the next image.

[ATTACH=CONFIG]2904[/ATTACH]

This one shows the difference when you change the surface area of the media from 1 (pic above) to 1000.... Notice the surface area of the bed required did not change?

[ATTACH=CONFIG]2906[/ATTACH]

In the above scenario, we doubled the volume of water and halved the density of the fish. In other words we are feeding the system exactly the same amount of feed.

EG 2000 liter of water with 10kg/1000 liters is still 20kg. Like 20kg of fish in the first scenario with 1000 liters of water.

If you change the tank volume to 4000 liters and 5kg/m3 (still 20kg of fish fed the same amount). The growbed is only 4.4m2 and the flow rate is still the same at 585l/h

When I change the tank volume to 10000 liter and 2kg/m3 (still 20kg of fish fed the same amount). The growbed is -6.1m2 and the flow rate is still the same. In this case we are talking about an exchange rate of once every 17 hours.....

To be clear they both have the same amount of feed input which is the key to any eco system, but the grow bed surface area has halved because there is twice the volume of water??...

So by this model we can feed 20kg of fish as long as we have twice the volume of water and half the amount of media and never change the flow rate. Very odd....

I find it very odd anyway.....

Perhaps I am missing something... no doubt someone with greater understanding will correct me.

Edited by Earthan Group (see edit history)

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This is why i could not come up with an answer to this question, i started off by finding out that the media being used provides half the surface are per m3 of media to K1, and tried to work back form there, knowing K1 provides a feed rate per litre of media. Where i got stuck is knowing the difference in efficency between k1 in a MBF to the effiency of lava rock in a grow bed.

So having concluded i can't calculate this for you i resorted to reading the the litrature i have available to me. Unfortunatly this provieded alot of information on the factors that affect stocking rate, but didn't even come close to suggesting a suitable stocking rate. So as you have not yet had a good answer i'll throw something out there for people to correct me on.

In my oppinion a 30gal system isn't really large enough to provide you with fish you can eat. Please correct me if i am wrong.

So it may be worth starting up with goldfish, and in 30gal (136l) then 10-15 gold fish may be a good starting point, as worst case if they get too big gold fish are easy enough to re home. Please any one who dis agrees with this speak up as this far poor Don has not been given much help with the question at hand.

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i tried editing my previous post but kind of messed it up..

keep in mind that all the formulas for kaldness or most media as filtration is looked at from an aquarists pov.. (amount of feed/sizing etc) and does not take into account the symbiotic relationship of the growbeds to plants to plant media

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I think I can help. The surface area of the media is in reference to the nooks and crannies of its surface. A glass marble would have a very low number. Gravel is 300, expanded clay is 250, and volcanic rock is 400. This number is only used in the calculation for people that want to use a (minimum)small media bed for a biological filter only with most of their growing done on rafts or NFT. More bacteria can fit into the same area if the media in the biofilter has a greater surface area. People using media beds for plant growth will always greatly surpass the few Liters of media it takes to do the biofilter job. (with the range for the most common media types between 250 and 400 a surface area of 1 would be impossible and an area of 1000 would be nearly magical.) http://en.wikipedia.org/wiki/Specific_surface_area

I think you'll see now that the biological surface area of the media does not change the area of plant growth required to remove all the nitrate from the water.

post-4431-13795788608872_thumb.jpg

Looks like mostly Tom Losordos work without credit....

From what I can see that calculator, which has been found incorrect once, the latest version is far from accurate.

So let's take a look....

[ATTACH=CONFIG]2905[/ATTACH]

This first one has 1000 liter tank with 20kg of fish. the surface area of the media used is 1. Changing that only changes the size of the bio filter results which you see in the next image.

[ATTACH=CONFIG]2904[/ATTACH]

This one shows the difference when you change the surface area of the media from 1 (pic above) to 1000.... Notice the surface area of the bed required did not change?

[ATTACH=CONFIG]2906[/ATTACH]

In the above scenario, we doubled the volume of water and halved the density of the fish. In other words we are feeding the system exactly the same amount of feed.

EG 2000 liter of water with 10kg/1000 liters is still 20kg. Like 20kg of fish in the first scenario with 1000 liters of water.

If you change the tank volume to 4000 liters and 5kg/m3 (still 20kg of fish fed the same amount). The growbed is only 4.4m2 and the flow rate is still the same at 585l/h

When I change the tank volume to 10000 liter and 2kg/m3 (still 20kg of fish fed the same amount). The growbed is -6.1m2 and the flow rate is still the same. In this case we are talking about an exchange rate of once every 17 hours.....

To be clear they both have the same amount of feed input which is the key to any eco system, but the grow bed surface area has halved because there is twice the volume of water??...

So by this model we can feed 20kg of fish as long as we have twice the volume of water and half the amount of media and never change the flow rate. Very odd....

I find it very odd anyway.....

Perhaps I am missing something... no doubt someone with greater understanding will correct me.

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I think I can help.

I think you'll see now that the biological surface area of the media does not change the area of plant growth required to remove all the nitrate from the water.

[ATTACH=CONFIG]2908[/ATTACH]

Mmmm not sure I am clear on this Jobney but thank you for trying to explain it too me.

The last two surface areas are in reference to the UVI system which comprises of floating rafts, so I don't think they come into play with a gravel bed set up.

I kind of expect that when I change the surface area of the media used, the "Surface area of bed for mineralization (at 300mm deep)" to change with it but it does not.

Sort of, when I use 20 mm gravel in a bed it will have less surface area than 10mm gravel so the total volume of the bed must increase as the surface area of the media in the bed is lowered, but this calculator does not do that.

Another example of what I am trying to poorly explain is:

I enter 1000 liters, 20kg/m3, 2% feed rate, 30% protein and 500m2/m3 surface area (but irrelevant). The bed size at 300mm deep required for mineralisation is 19.5m2.

If I change the surface area of the media in the gravel bed the bed size does not change

I find it very odd....

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This calculator is designed to give you a gravel bed size based on UVI feeding rates. UVI feeding rates give you a predicable plant growth area vs how much and type of fish food goes in. Those are indeed the bed sizes for media/gravel beds. There is a but. The instructions say to use the largest bed output given and that is often the "bed required for mineralisation". It does not tell you the area of this bed size that you would actually install plants. It would be a little higher then the UVI planted area but not that much more. Most people on this forum remove solids or mineralise the solids outside the system and then pump the minerals back in. Not many around here use the growbeds as a fish septic tank.

The same area of Rafts grows the same number of plants as a media bed or NFT. Leafy greens area at the bottom is how big your growbed would have to be for those types of plants to keep nitrate at a steady state. Media surface area is only used in the calculation for biofilter size. Think of the media surface area as housing for bacteria. (that's why the output for biofilter is in Liters as it is dependent on "Specific surface area"). The surface area of the media type does not affect mineralization. Mineralization is a function of being captured in the growbed with microbes and worms working it over and time. Bumpiness of the media type has no play here. The surface area of the media type also has no play on plant growth. The macro qualities of the media type is a variable in plant growth but when we say "Specific surface area" we are only referring to the micro texture. 1 liter of (smooth) marbles having a lower number then 1 liter of (porous) expanded clay.

There is a PDF with more information on the sizing model page. called "The "How to use..." document" http://www.aquaponic.com.au/backyard.htm

http://www.aquaponic.com.au/Aquaponic%20media%20bed%20sizing%20model%20explanation.pdf

Mmmm not sure I am clear on this Jobney but thank you for trying to explain it too me.

The last two surface areas are in reference to the UVI system which comprises of floating rafts, so I don't think they come into play with a gravel bed set up.

I kind of expect that when I change the surface area of the media used, the "Surface area of bed for mineralization (at 300mm deep)" to change with it but it does not.

Sort of, when I use 20 mm gravel in a bed it will have less surface area than 10mm gravel so the total volume of the bed must increase as the surface area of the media in the bed is lowered, but this calculator does not do that.

Another example of what I am trying to poorly explain is:

I enter 1000 liters, 20kg/m3, 2% feed rate, 30% protein and 500m2/m3 surface area (but irrelevant). The bed size at 300mm deep required for mineralisation is 19.5m2.

If I change the surface area of the media in the gravel bed the bed size does not change

I find it very odd....

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Thanks for your patients Jobney.

If I take the following senario:

1000 liters water

20kg fish / 1000 liters of water

1% feed rate

36% protein

Results for bed size are:

Leafy greens = 5m2

Fruiting = 2.7m2

200 grams of feed per day is going into the system

By the feed reference from UVI noted on the calculator for leafy greens and fruiting is 60grams and 80grams per m2 per day respectively.

200 grams divided by 60 = 3.33 leafy

200 grams divided by 80 = 2.50 fruiting

My numbers above are from UVI using a 36% protein feed for a floating raft.

It is odd the square meters for a floating raft from the calculator are what is considered the size for a gravel bed as they should be very very different.

It gets even more weird when you only change the protein content up and down, the floating raft recommendations (gravel beds.....) sizes only change when the protein is above or below 33%. That can not even be close to right if we are talking about the nutrient content of the water and the capacity for TAN removal. If the protein levels rise, so should the required area for growth... well at least in my mind lol.

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No further clarification on this? This calculator is a mystery to me.

It seems the bio filter part has a built in 10% which may be for passive nitrification, walls, bottom, pipes etc, but I am not sure why it is there. I kind of expect a backyard calculator to not apply any passive nitrification to provide at least that much stuff up factor. But there is no note to suggest that is the case. I would prefer to have more but can not make that change in the calculator.

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Sorry, I've been getting ready for a vacation.

Yeah, the UVI ratios are designed at a set protein % and although he is attempting to adjust them to the protein level input they have very little "push" on the bed sizes especially on smaller systems. (the numbers only changing once for the whole range of 1% - 100%) The calculations he uses for biofilter and mineralization are stand alone and move a lot more when protein levels change. The only issue I really have is that his mineralization bed size is not a plant planting recomendation. If you planted the whole thing you may have too many plants. Most people on this forum remove solids and don't mineralize them or mineralize them in a separate aeration tank and reintroduce them later. (UVI removes most, only mineralizing a fraction.)

The good news is that in the real world the margin of error in our little man made ecosystems is greater then any anomalies in the model. The model is attempting to assign mathematics to biological processes that are very complex. When inputs are kept in the normal ranges and away from any extremes that you would never actually build into a system, the media bed sizing model does a decent job. It's especially good considering that the alternative is some made up rule of thumb ratios like 1:1 or 1:2 that don't take in to account stocking densities and assume media bed volume is the same as media bed grow area. I'll even go out on a limb and say that most people with back yard AP systems are "eyeballing" their stocking densities and feeding rates. So for back yard use the sizing model is going to get you into the ballpark nicely. Better then someone telling you, "1:1 but maybe 1:2". Imagine if a diabetic injected insulin with that margin of error. :)

In regards to the biofilter question I don't have the time to look into it right now but take comfort in that if you are using a growbed for plants that your biofilter is covered. The liters needed for biofiltration is a tiny tiny fraction of a planted media bed. I would just ignore it. It's there for people that are using DWC and a gravel bad for a biofilter. I've never seen anyone actually do it that way. UVI does not even have a biofilter component. They've stated that enough bacteria live on the rafts to do the job. If you are like me and a lot of others you may be looking into the K1 media moving bed biofilters. They are easy to make and usually oversized. Put them in after solids filtering for easy system insurance. Nice if you ever need to remove the gravel beds for cleaning. The downside would still be that you can't really control where your bacteria grow so you can't make them stay in the biofilter you built. Remove an established media bed and you might have a slight mini cycle. At least a moving bed biofilter once established would be quick to take the new load.

No further clarification on this? This calculator is a mystery to me.

It seems the bio filter part has a built in 10% which may be for passive nitrification, walls, bottom, pipes etc, but I am not sure why it is there. I kind of expect a backyard calculator to not apply any passive nitrification to provide at least that much stuff up factor. But there is no note to suggest that is the case. I would prefer to have more but can not make that change in the calculator.

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