Backyard Aquaponics
A place to discuss aquaponics

How much do you think the smaller fish under 20 grams would weigh all together?

I am trying to calculate the total amount of food this system will be using every day when its fully in operation.

I estimate that it will take 1003.2 grams of food per day.. Does this sound ok?

Take off your shoes and do the math. Use the growth chart.

(30 fish x 1g) + (30 fish x 5g)
= 30 + 150
= 180g of fish at -under- 20g.

These smaller fish require feeding at higher rates:
(30g x 20%) + (150g x 10%)
= 6g + 15g
= 21g of food each day to feed the smaller fish.

Larger fish get fed at lower rates, per the growth chart linked on the previous page. Your turn to do the math.

....and just having a little mercy....

Doing fast estimating, figure 40kg of fish fed at roughly 3%. That makes 1.2kg or 1200g. Since I rounded up on the kg of fish, 1200g is a touch high. So yes, 1003.2g sounds about right.

So my system will be fed 1 kg for food every day and produce about 37g of ammonia produced every day. So .9g of ammonia can be processed by 1 square meter of surface area. So I would need about 42 square meters of biologically active medium to process all this ammonia.

Gravel has, say, 150:1 surface to volume ratio. So, 1 cubic meter of gravel would have 150 square meters of surface area.

150/42 =3.57 So just over 1/3 of a cubic meter of gravel will process the ammonia.
1 (cubic meter) = 61 023.7441 cubic inches
61 023\3.57 = 17093 cubic inches
17093 / 231 (cubic inches per gallon) = 74 gallons of gravel....
WOW, seems like a pretty low amount of media to process all the ammonia !

Is my math correct?

Seems off to me too. I have 150gal of media and can only feed 50g per day. Let me get out the calculator....

I must not have the correct surface to volume ratio for gravel.
114 gallons for 100:1 ratio.. or Perhaps I have the grams to surface area wrong for ammonia conversion.

I think part of the problem is in the surface area calcs. Here http://wernersponds.com/biofiltermedia.htm I find that 1/2" gravel has 90 square feet of surface area per cubic foot of volume. So let's get that in to metric: We'll use the converter here: http://www.sciencemadesimple.net

That gets us to 8.36:0.03 or 279 square meters : 1 cubic meter. So I think your media rate is low, but I'll switch back to your numbers.

150/42 = 3.57 as you said, but when you invert it, you get 0.28 of a cubic meter. Let's work with 0.3 cu m, and let's not go through the inches thing.

0.3 cu m = (100mm x 100mm x 3) = 300 liters
300 liters/3.8 = 78.9 gal

So your math is good (albeit painful), but there has to be another assumption that is off....

Ah ha. Go back to the werner link, in the 'If you like math' section. They suggest calculating based on 1sqm of surface processing 0.2g ammonia per day, not 0.9. So we're off by a factor of 4.5.

78.9 x 4.5 = 355 gal of media.

OK, wasn't that fun??? But I still don't like the answer. I can tell you that my 150 gal of gravel will process the ammonia from 50g of food each day. If I feed any more than that, I get nitrite spikes. That means to process 1kg of food, I would need 3000gal of media. And interestingly, that brings us right back to the approximate rates already quoted. I wonder if we messed up the decimal point up there somewhere....?

I will have 595 gallons of water in this system. It will have grow beds out doors for warm weather and a bio filter indoors for cold weather with NFT plant area using windows and grow lights. I will, of course, have stands for the tanks.

Here is the lay out that I will be able to fit in one end of my hatchery.

3000 gallons of media for 1kg food. WOW! No one has that much gravel on their system.. That would be a 5:1 ratio for this system..

Perhaps, what Im not looking at is how much surface area is gummed up by the poo?

Oh! and thanks Janet for taking the time to look that up!

There's theoretical results, conservative planning and then what really happens. Oh *%$#@*!!!

Is there anyone else on this forum who knows how many grams of food they can feed before they get a nitrite spike? If so what is that number and how many gallons of gravel do you have?

How many fish do you have Janet? How many of grams of fish do you have?

Dan

Unsure whether you have this link http://srac.tamu.edu/fulllist.cfm

The one you are probably interested in is SRAC 454

These are commercial but very good and courtesy of Michael F

I have maybe 10-15 fish that are about 400g and 30 fish that are perhaps 100g, so let's call that 8000g or 8kg of fish with 570 liters of beds. I run a lower stocking rate than some, I suppose.

What do you think of this? 400 gallons of gravel as a pre-filter and grow bed followed by a 5 gallon fluidized sand filter; using super fine sand blasting sand.