Backyard Aquaponics
A place to discuss aquaponics

There are many ways to calculate how many fish your system can hold, or how much veggies you can grow, how much you should feed your fish or even how big the pump should be. In this topic I'll try to explain how I think this is all linked together and what the ratios are.

Also, you can just skip all this and use the excel sheet below to calculate the minimum and maximum amount of fish and fish food for your system.


Calculations of ratios
I've read much about the 6:2:1 or 6:200:100 ratio. It means that you can have a maximum of 6kg of fish for every 200L of growbed or 100L of fish tank (which ever is the lowest).
This maximum is for an optimal system with a growbed of 30cm deep, but since you'll have to work with whatever you get I translated the ratio to square meters of growbed, so you can use it also for growbeds that are not the optimal 30cms deep.
6/(200/(3*100))= 9kgs of fish per square meter of planted growbed.
In this topic VB wrote that 500L of growbed was just enough to keep up with 150-200g of fish food a day. Using that data, I found that the 6:200:100 ratio only works when you're feeding no more than 200/(500/200*6*1000)*100%= 1,33% of their weight a day. So I tried to translate that to a ratio that includes the fish feeding ratio.
In this topic Caribean-grower wrote that it takes between 60-100g of fish food per square meter of planted growbed per day. VB’s post suggests an absolute maximum of 150/(500/(3*100))= 90g to 200/(500/(3*100))=120g per square meter of growbed per day. So 60g per sqm growbed is the minimum required for the plants, and 120g per sqm is the maximum the plants can handle.
So if you have 1 square meter of growbed, and want to feed at 2% fish weight, the absolute maximum amount of fish the growbed can support is 6kg, and the minimum amount of fish you need to support the growbed is 3kg. At 4% feeding, you can only need 1,5kg of fish to keep the growbed at optimum growth, but you can support no more than 3kg of fish.
The 6:200:100 ratio only works with a sufficiently large pump pumping the water around. The consensus is at least the growbed volume once an hour. For the optimal growbed this is 300L/h per square meter, at maximum stocking this is 100L/h per 3kg of fish, and at maximum feeding (1,33%) this is 250L/h per 100g of fish food.


How to calculate when starting a new system
Either use my excel sheet which will calculate everything for you, or:
- Calculate the surface area of your growbed that will be planted (square meters).
- Multiply this by 60 to find the minimum fish food per day going into the system to keep the plants happy (in grams)
- Multiply this by 120 to find the maximum fish food per day that the plants can process (in grams)
- Divide the minimum fish food value by the feeding rate to find the minimum amount of fish your system needs (in grams)
- Divide the maximum fish food value by the feeding rate to find the absolute maximum amount of fish your plants can keep up with (in grams)
- Check if the pump puts out at least 250L/h per 100g of daily fish food (at the given head)
- Check if there’s at least 100L of fish tank per 6kg of fish
- Check if there's no more than 9kg of fish per sqm of growbed


So I used the following values:
Max fish per 100L tank: 6kg
Max fish per sqm growbed: 9kg
Optimal growbed depth: 30cm
Min fish food per sqm of growbed: 60g
Max fish food per sqm of growbed: 120g
Min 'optimal growbed' turnover per hour: 1x

If you disagree with those values, but still want to use the excel sheet, you can easily change them at the bottom of the sheet.


I hope this is of help to somebody.

To use 200L/55gal blue barrels or drums in the excel sheet, use:

Half blue barrel, cut vertically: use 'rectangular growbed(s)' and fill in length 88cm, width 56cm, depth 22cm (or just use 0,49sqm each).
Half blue barrel, cut horizontally: use 'round growbed(s)' and fill in diameter 56cm, depth 44cm (or just use 0,25sqm each).
Blue barrel as fish tank or sump: use diameter 56cm, depth 88cm.

Bloody brilliant! I wonder if we can incorporate other knowns - like the growth rates of various fish from the silver perch thread here viewtopic.php?f=25&t=3407&p=125853&hilit=growth+graph#p125853

Thanks Xzorby.
Just what I needed!

Hamish, I haven't been able to incorporate growth rate, but I did manage to incorporate some other things, so I made a version 2 of the excel sheet. I'd like to update the first post with this new version, but I can't edit the post

This sheet now also uses:
- Fish food protein content
- Fish conversion rate (FCR)
And optional:
- Peeponics!
- Other fertiliser.

Screenshot:


Instructions: fill in your growbed, tank and sump dimensions in the yellow boxes, or just fill in the orange boxes if you already know the area and volume. Then fill in the green boxes (if you don't know the FCR, you can keep it at 1,7). You can also fill in the blue boxes if you use other sources of nitrogen besides fish food.
The sheet then calculates for you:
- minimum, optimal and maximum amount of fish (kg), fish food per day (g) and total N per day (g)
- if your pump is sufficient
- if your tank and sump volume are sufficient



I would like to make this sheet as accurate as can be. It would be great if people with established systems tested the sheet and replied here, to see if the values used are accurate!

NICE!

I love Excel - it is so versatile! Keep up the good work - this spreadsheet will get better and better I am sure!

I am thinking of adding something like this to to your spread sheet track water quality:

viewtopic.php?f=18&t=2706&st=0&sk=t&sd=a&hilit=graph&start=114

and something like this to track fish growth (weight/length) in a system over time.

viewtopic.php?f=25&t=3407&p=125853&hilit=Silver+Perch+growth+graph#p125853

and perhaps journal entries to add things that have been planted, feed, fish/plant observations, pest controll etc.

Adding these things it might be possible to create a sort of 'system monitor' spreadsheet with your spreadsheet as the basis.

I think I will be using urea to cycle my system as done here:

viewtopic.php?f=18&t=2706&st=0&sk=t&sd=a&hilit=graph&start=98

Kenny has been kind enough to post his graph excel spreadsheet here:

viewtopic.php?f=18&t=2706&st=0&sk=t&sd=a&start=269

A new version of my spreadsheet! This version lost the peeponics and other fertilisers input functions, but became more accurate and easier to use. I have been thinking about adding an RSG filter option as well as some other things, but that wouldn't be entirely aquaponic. The calculator is now purely aquaponic again - no other inputs than fish food an no other output other than fish and veggies.


Instructions: Fill in your growbed and fishtank dimensions in the yellow boxes, or just fill in the orange boxes if you already know the area and volume. Either leave the green boxes as they are, or change them for a more accurate calculation.
The calculator will then calculate for you how big your pump should be, how many kilograms of fish your system can handle and how much food you can throw into your fishtank every day. It gives three different approaches; a low-input system (just enough input to get good plant growth), a balanced system (lots of fish and lots of veggies) and an intensive system (fish-oriented).


Input: growbed and fishtank dimensions
Optional input: FCR, daily feeding rate, fish food protein content, desired relative stocking density, growbed media volume percentage
Output: Fish food per day, total amount of fish, minimum pump output at growbed head

Screenshot:



As soon as I've learned how to program, I'll turn this spreadsheet into an .exe that is easier to use and has more options. I might even make it into a complete program, with more fish options, predictions and possibly some of the things Hamish suggested to store water and fish values into a journal with nice graphs etc. But that'll take time.