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PostPosted: Feb 1st, '19, 14:06 
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danny wrote:
more ammonia is released from the breakdown of solids than the amount that is diffused directly from the fish's gills.

Do you have any info, or links to info on that?

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PostPosted: Feb 1st, '19, 20:33 
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Actually I messed up on that statement, apologies. I must have confused it with something else, or just mis-remembered it . Having re-checked the figures I read that

"it is estimated that 7-32% of the ammonia in fish farm waste water is associated with organic solids."

The info comes from course material from my studies, I can't provide a link unfortunately.

Also, "30-84% of waste phosphorous is commonly carried by suspended solids." - this may have been what I got confused with.

I think BOD (biological oxygen demand) is important here, as the breakdown of solids by heterotrophic bacteria will use up oxygen, which may ultimately be the limiting factor when it comes to stocking density.


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PostPosted: Feb 1st, '19, 20:46 
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This link is all I can find so far. It describes the content of solid waste sludge from salmon farming:

https://www.researchgate.net/publicatio ... for_salmon


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PostPosted: Feb 1st, '19, 21:39 
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danny wrote:
Actually I messed up on that statement, apologies. I must have confused it with something else, or just mis-remembered it . Having re-checked the figures I read that

"it is estimated that 7-32% of the ammonia in fish farm waste water is associated with organic solids."

The info comes from course material from my studies, I can't provide a link unfortunately.

Also, "30-84% of waste phosphorous is commonly carried by suspended solids." - this may have been what I got confused with.

I think BOD (biological oxygen demand) is important here, as the breakdown of solids by heterotrophic bacteria will use up oxygen, which may ultimately be the limiting factor when it comes to stocking density.
based on that, I guess a rough estimate of 15% less ammonia if one removes solids could be feasible. In that case the 20-25 litres of wet media per fish becomes around 17-22 litres. I guess the only way to really know is to keep an eye on my ammonia and nitrite readings


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PostPosted: Feb 1st, '19, 23:44 
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What kind of system are you running?

Are you also removing suspended solids?

In commercial RAS systems with aeration and very effective solids removal Tilapia stocking densities can be even higher than 120kg/m3.

Aqauaponics rules of thumb are on the conservative side for obvious reasons, and account for mineralization of solids within the system.

If you are running DWC with effective solids removal things are definitely a little different. Some massive commercial AP DWC systems don't even have bio-filters as enough surface area is supplied by the roots of the plants.


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PostPosted: Feb 2nd, '19, 23:57 
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danny wrote:
What kind of system are you running?

Are you also removing suspended solids?

In commercial RAS systems with aeration and very effective solids removal Tilapia stocking densities can be even higher than 120kg/m3.

Aqauaponics rules of thumb are on the conservative side for obvious reasons, and account for mineralization of solids within the system.

If you are running DWC with effective solids removal things are definitely a little different. Some massive commercial AP DWC systems don't even have bio-filters as enough surface area is supplied by the roots of the plants.


I'm running a simple chop-and-flip IBC with a flood and drain growbed and an RFF in between. I get that the commercial guys do all kinds of fancy magic on their systems, but I guess the majority of us on the forum have relatively basic backyard systems.

The first post of this thread recommends 3kg of fish per 100l of wet media while the IBC of Aquaponics suggests 1 fish per 20-25l of wet media. I guess I'm trying to determine the effect a simple RFF would have on those numbers.


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PostPosted: Feb 3rd, '19, 02:06 
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Perhaps a bit, but I personally wouldn't be comfortable straying too far from the rules of thumb unless I had suspended solids removal too, i.e. a moving media filter or a static up-flow filter etc. The addition of this would also provide a good deal more bio-filtration.

I can't talk from experience however. Perhaps someone else can...


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