Backyard Aquaponics
A place to discuss aquaponics

14 half barrels = 7 full barrels at 55 gals each = about 385 gallons of pea gravel.

385 gallons of pea gravel / 1 pound of fish to 5 gallons of media = 77 lbs. of fish

Only count the media that gets wet and acts as a filter when doing this calculation. Of the 55 gallon barrel you might only wind up with 40 gallons of media and all of it won't actually get damp.

did they say the barrels were 55 gallon?

in any case, that amount of fish weight is at max grow out, do not stock 22 lb of fingerlings because the system would be very quickly overloaded.

Now I didn't look back over the math to figure out if your numbers were correct or anything. But if you plan to grow your tilapia out to 1 lb each and if you figured out your system could support 22 lb of fish then you stock 22 fish.

Now that recommendation of 1 lb per 5 gallons of media is a bit heavy on the stocking (it is like MAX stocking)
a more conservative number is 1 lb of fish per cubic foot of media (about 7.5 gallons of media.)

For most types of fish I count one fish as one lb (no matter what their size to start with) but I grow channel catfish so I start off figuring they are 2 lb each and I thin them as they get big since they can easily grow to 5 lb in a year. (I never really understood this idea that tilapia grow fastest since the biggest tilapia I ever got was 2 lb and I had that one two years, I've had a channel catfish get to 10 lb in two years before. Trick is if you are not heating your water, the catfish keep eating down to about the temperatures that start killing tilapia.)

No they didn't but everybody uses the 55 gal drums, you wouldn't use a 30 gal, nor the 85 and 110 gal. they are specialty drums and most have the removal tops. Actually the 55 gal drums will hold more than approx. 57.5 gals. All drums are that way.

So if you have 40 gals. minus 2" from the top as being dry, and take into account the air pore space, How many gals fish water to each 1/2 barrel??????

..
And a barrel on it's side might have FAR more material in the top two inches of dry stuff, than the next two inches.. ie.. the shape is determining the volume..
..
.

I wouldn't get too hung up on the dry vs wet provided you are flooding and draining and only keeping the top inch or two dry. If you don't fill the barrel up as full as you can, then you need to figure in the missing media volume.

We want to keep the math and figuring relatively simple.

I have seen people use smaller barrels so it is best to double check assumptions.

30 Gallon Closed-Head Drum - 19-1/4" Dia x 30-1/4"H supports 42 lbs. of fish

14 half barrels = 7 full barrels at 30 gals each = about 210 gallons of pea gravel.

210 gallons of pea gravel / 1 pound of fish to 5 gallons of media = 42 lbs. of fish.

As for assumptions, the name of the game is "Max Production Area" and 30 gals is a waste of time.

If I was to do a system using 1/2 drums, I would use the 77 gal size 44.5" tall x 23" dia.

But, I neither use a 1/2 barrel system, My GB's are Min. 4' wide, Max. 8', Lengths are Min. 8' and Max up to 96'

Only need 6' deep soil-less mix, and a water supply, with or without AP water of 5 gals 4' wide beds up to 10 gals. on the 8' wide bed, per linear foot of length.

Ouch watch how you state that first line!!!!!!
a 30 gallon drum doesn't support 42 lb of fish no matter what way you do it. I suspect that isn't how you meant to state it based on the rest of your post though but watch out for people who skim read!

Are you going for max production of fish or veggies? It really doesn't take that much fish to support quite a bit of veggies so you can always run less fish and more gravel bed than the numbers I sometimes see people trying to run.

If your numbers suggest you can handle a max of 42 lb of fish, start with only 42 or less fingerlings, I know it will be less then 42 lb to start but that is OK since the system has to mature before it can handle the max load AND smaller fish tend to eat quite a bit in relation to their body weight and usually a far higher % of protein. So it is OK to start out with less weight of fish in the system, especially if it is a new system and you are having to ask how many fish can it support the answer is always less until you no longer have the need to ask the question. Otherwise you risk killing all the fish when the levels spike in a new system.

The numbers are from the other persons formula, not mine.

I start with 500 fish in a 200 gal/ tank. by the time they are 3-4" there is less than 50, they have been sold to others that can't get them. by the time they are 5-6" the numbers are even way less.

But I don't raise Talipia or Catfish, I raise Koi.

Terry

I have a 4x8 grow bed, so 32sqft of growing space. I have a 100 gallon rubbermaid tank....how many blue tilapia would i need? just starting my system off, thanks!

"I have a 4x8 grow bed, so 32sqft of growing space. I have a 100 gallon rubbermaid tank....how many blue tilapia would i need? just starting my system off, thanks!"

Posters User thread here >> viewtopic.php?f=18&t=27897&start=30 for specific replies.
**Text below copy for example only**.

100 Gallons ~ 400 Litres is a pretty small fish tank.
You would really only be looking at around 15-20 medium goldfish for example.
(comfortable conservative stocking)

At the top end....
FAO **recommended** are 10-20kg of fish per 1000L (1-2kg per 100L)
TClynx is *max* at 3kg per 100L (9-12kg)

400L so 4-8kg.... so you are really looking at around 15 300-500g fish.

grow bed is 4' x 8' (1.2 x 2.4m) - depth presume 10' (250mm) ~ 0.7m3 media (sorry metric here).
650-700L is 40L wet media / fish @ 15 - so conservative (=good).

Fish tank will be the limiting factor. With experience one can probably stock slightly higher.
but for any system it is best to **start out with lower stocking levels**.

** FAO reference can be found here....http://www.fao.org/3/a-i4021e/index.html (there is link there for the PDF version).
page 125

What would be the equivalent volume of bioballs for 25l of leca in terms of filtration capacity?

How would the addition of an RFF to remove solids affect the 25l of wet grow bed media per 500g fish rule of thumb? Does removing the solids allow for higher stocking, or does the solid removal not really change this?

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Solids removal does allow for higher stocking density to bio-filtration medium. Indeed supposedly more ammonia is released from the breakdown of solids than the amount that is diffused directly from the fish's gills.

To work out to what extent requires some pretty intense mathematics.

Here's a link to some useful info http://biofilters.com/websize.htm

More can be found searching "bio-filtration surface area required" etc