Backyard Aquaponics
A place to discuss aquaponics

Hi



55 gallon drums are 200 litre, https://en.wikipedia.org/wiki/Drum_%28container%29
cut them in half, that would be 100 litre, if filled to the top, so your calculations are wrong

cheers

Each half barrel would contain only ~100l of wet media, IF they were full and wet to the top, so your calculations are somewhat overestimating your media volume. In the photo, they appear to be only half full, so at that stage you probably had, considering the shape of the barrels, less than 150l of media in total.
If you have added more to fill them up, you might get nearer to 400litres.

I hate it when I think I did everything right and it is proven wrong.

I used this site to do the conversion
http://www.onlineconversion.com/object_volume_cylinder_tank.htm

The height is 880mm the diameter is 610mm

according to the site that is 257177057 cu mm
or converted to liters at website
http://www.metric-conversions.org/volume/cubic-millimeters-to-liters.htm
equals 257 liters.

Halved that is 125 liters. Ok, so say that the 2" of space to the top of the half barrel accounts for 25 liters in every GB giving 100 liters per bed. There are 14 GB's totalling 1400 liters of media.

I've manually filled each grow bed with 2 five gallon and 1 gallon bucket of water. Each GB reaches about 11 gallons when it starts to auto siphon.

Now that I know I have 1400 liters of media with 1 fish per 25 liters of media, I'm looking at 56 fish full size fish, am I correct. Full size would be about 20 ounces or 600 grams.

Hi again
257 liters = 67.8922175 US gallons

What kind of drums do you have ?

It is this ?

They are blue food safe barrels marked 55 USgal

55 (small US) gallons = 208 litres

This thread has had a fairly extended life for what is a very clear cut issue IMO...

Insufficient bio-filtration (wet gravel) causing ammonia to build up to point that is toxic to the fish.

As a couple of people have already pointed out, at a pH of 8.8 and water temp of 21C, even the slightest amount of Ammonia would prove toxic to your fish... even well below the minimum measurable level on most test kits of 0.25ppm... So an Ammonia level of 2.0ppm was always going to create fish soup.

If the drums are a 205L (pretty much standard) then when cut in half lengthways, filled with gravel to about 25mm (1") from the top, and flooded to about 40mm-50mm (1¾"-2")from the surface of the gravel, you will have a maximum of around 70L of wet gravel per grow bed.

For fast growing fish you need 25L of wet gravel, so if set-up as described above, giving a combined wet gravel total of around 280L, or 300L max’, it would allow a maximum safe fish stocking capacity of about 12 fish...

...but the maximum gravel level in your drum halves looks like it’s well below the 1” mentioned above, it looks more like you have about 4” of freeboard. Taking into account the curvature of the bottom of the drum (grow bed) you might find your wet gravel volume is more like only 40L per grow bed, 50L at a stretch.

So working with the glass-half-full volume of 50L of wet gravel, that's a total volume of 200L for the four beds, which IMO would give you a maximum safe stocking capacity of around 8 fish.

Some people say that Tilapia can handle poorer water conditions than most other fish, but I'm sure that's probably referring to suspended solids and D.O. levels, not Ammonia levels... but let's just say you could get away with only 20L of wet gravel per fish, that's still only a maximum safe fish stocking capacity of around 10 fish... unless I’m missing something with your system.

We keep losing count of the number of grow beds, there are 14 half barrel grow beds. at 70 liters per bed that is 980 liters. divided by 25L per fish. that is 39 fish.

I just went out and emptied one of the grow beds into 5 gallon buckets two filled to the top and one about 2.5 inches down from the top of the third bucket. So if I call that 11 gallons I am looking at about 52 liters in each grow bed. So I'll be conservative because obviously this is not an exact science and go with 50 liters per GB. (50 x 14)/25 = 28 full grown fish which will weigh approximately 21 ounces or 600 grams each.

I am putting together a second AP system in an old greenhouse. By next week I should have it cycling, without fish, and 10 GB's. I'll allow it to cycle with some gold fish in the constant flood GBs to get some ammonia and get the PH solid and the bacteria in the beds established, then will take the extra tilapia out of the existing FT and give my grandchildren back their goldfish. In that system the constant flood GBs will have no media, and will have water hyacinths in one and duckweed in the other. These tilapia are now between 3" and 4". or 76mm to 100mm.

I now have some rules of thumb for my system and I think it will result in a healthier environment for plants and fish. Thanks for your patience and help

Ed

Correction on the above, the 2+ buckets would be around 14 gallons or 52 liters.

I was referring to, and commenting on the OP's system and water conditions.

Understood

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Surely we know how many BAGS of clay was added. Oh such speculation and calculations..

It seems the half barrels are half full and by the shape that would likely be about a 1/3 of actual media.. (total guess)

Do you know how many bags of clay were used per unit ..
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Sorry, I used pea gravel and bought it by the ton. Each half barrel took two completely full 5 gallon buckets and a third bucket that was about 1.5 inches from the top. So approximately 14 gallons of pea gravel for each half barrel.

I just went out and emptied one of the grow beds into 5 gallon buckets two buckets filled to the top and a third bucket about 2.5 inches down from the top of the third bucket. So if I call that 14 gallons I am looking at about 52 liters in each grow bed. So I'll be conservative because obviously this is not an exact science and go with 50 liters per GB. (50 x 14)/25 = 28 full grown fish which will weigh approximately 21 ounces or 600 grams each.

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OK .. so no arguments about the volume of media..

I know how little it helps the initial loss..
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