Aquaponics Digest - Wed 01/19/00
Message 1: trout and lettuce
from "Marc Laberge"
Message 2: Re: trout and lettuce
from Ronald Polka
Message 3: nutrients in fish waste
from "Marc Laberge"
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Subject: trout and lettuce
From: "Marc Laberge"
Date: Wed, 19 Jan 2000 11:09:55 -0500
Paula wrote,
"What size plants will you transplant into your raft system? Will you be
removing solids?
I wrote,
>I read in the aquaponics journal an article by Gorden Ceaser about
hydroponics in England in the early 50's using sheep tea...can anyone tell
me if this can be done in an aquaponics system using fish feces.
Paula wrote
I've not read the article, but unless I misunderstand the question, that's
exactly what aquaponics does. The type of delivery system will have a lot
to do with system design, though.
The reason I asked about the "tea" is because I do not want to leave the
fish..."waste", in the water for too long of a period. I am working with
rainbow trout and char ( their gills are extremely fragile to high TSS), yet
if I remove all the sludge I am removing nutrients from the plants. The
solution I want to try is to control the amount of time the "waste" will be
in the water using a sort of sock/bag. The idea being the waste will be
removed and placed in a sock for a certain period of time , as a sort of tea
bag in the water.The system will be a sort of rotating tea bag system. This
should help control TSS , allow me to control the amount of time the waste
is in the water ,allowing for maximum nutrients to be released and keeping
a control on the sludge break down. i.e. control of water quality once a
balance dependent on temperature and quantity of waste is achieved.
William wrote
I too use net pots with rafts. Haven't thought of that question. Are you
using the short 2 inch pots, about 2 inches deep? (I have seen 3 inch deep
too.)
The net pots I am using are both types, the 2x 2 and the 3 x 3, as you said
I guess the larger pots are too large and deep. I did not want to place the
rock wool into the net pots of fear that the break down of the rock wool
would eventually end up in the trouts gills. The transplants will be either
2 weeks old or 2 inches high...haven't decided...need more advice on this.
Any advice or comments are always greatly appreciated.
Marc Laberge
Mont "Freezing" Tremblant.....temperature here is -22 F
Qc.,Canada
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Subject: Re: trout and lettuce
From: Ronald Polka
Date: Wed, 19 Jan 2000 10:48:55 -0700
Marc
I would think that you would want to remove the solids from the system as
soon as is practical and rely solely on the nutrients that are already
dissolved. My experience has been that the longer the solids remain in the
culture water the more they break down into small particulates. Presumably
this is what causes trouble with the gills relative to TSS. In an
aquaponics system the feces drift around in the fish tank until removed.
During this time any nutrients that will leach out have a tendency to have
done so, leaving fibre, inorganic wastes, and non-leachable nutrients
behind in the fecal matter. I wonder if this solid waste has much left in
it to contribute to a hydroponic setup. I can see where it could still be
usable for soil based crops but I question its efficacy for a water based
system. The advantage of using manure teas brewed in bags is that the
manure comes from cattle/sheep/chickens where the manure is allowed to dry
somewhat before being bagged and used. There is no prior leaching of
nutrients as occurs in fish wastes. Ammonia levels in aquaculture water are
a clear indicator of this leaching. Solid wastes are best removed and
utilized elswhere such as on the garden or in a compost pile. If solids are
allowed to accumulate in the system they will also use oxygen as they
decompose.
One of my systems uses an artificial wetland for treatment of the
recirculation water in tilapia and largemouth bass tanks. The wetland
converts ammonia via bacterial action and the growth of canna lilies and
water plants in the subsurface flow wetland.
In order for this to work properly the waste stream goes through a settling
tank first where the collected feces can be flushed out of the system
daily. This enhances wetland operation and prevents clogging of the
interstitial spaces. Solids removal in this system is critical for
maintaining efficient operation.
A flow through system that I operated for awhile used a horizontal flow
settling tank for waste removal. I planted lettuce and watercress in that
tank using a floating raft setup. The system worked relatively well but
seemed to go through cycles with the cress. I suspect that there may have
been times when the dissolved oxygen level in the settling tank was below
optimal levels when solids buildup in the settling tank reached a critical
point.
>"What size plants will you transplant into your raft system? Will you be
>removing solids?
>
>The reason I asked about the "tea" is because I do not want to leave the
>fish..."waste", in the water for too long of a period. I am working with
>rainbow trout and char ( their gills are extremely fragile to high TSS), yet
>if I remove all the sludge I am removing nutrients from the plants. The
>solution I want to try is to control the amount of time the "waste" will be
>in the water using a sort of sock/bag. The idea being the waste will be
>removed and placed in a sock for a certain period of time , as a sort of tea
>bag in the water.The system will be a sort of rotating tea bag system. This
>should help control TSS , allow me to control the amount of time the waste
>is in the water ,allowing for maximum nutrients to be released and keeping
>a control on the sludge break down. i.e. control of water quality once a
>balance dependent on temperature and quantity of waste is achieved.
>
>The net pots I am using are both types, the 2x 2 and the 3 x 3, as you said
>I guess the larger pots are too large and deep. I did not want to place the
>rock wool into the net pots of fear that the break down of the rock wool
>would eventually end up in the trouts gills.
>Any advice or comments are always greatly appreciated.
>Marc Laberge
>Mont "Freezing" Tremblant.....temperature here is -22 F
>Qc.,Canada
>
>
Ron Polka
Southwest Technology Development Institute
New Mexico State University
Box 30001, Dept 3SOL
Las Cruces, NM 88003
rpolka@nmsu.edu
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| Message 3 |
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Subject: nutrients in fish waste
From: "Marc Laberge"
Date: Wed, 19 Jan 2000 19:12:55 -0500
Hello Ronald,
Im not sure if I agree with you on the nutrients left over in fish feces
; in recirc aquaculture systems 80% of phosphorous and 20% of ammonia can be
removed with proper filtration. i.e. this means 80% of phosphorous and 20%
of ammonia is in the solid form. The longer the solid is left in water , the
more P and N will leach out ( and probaly many more goodies ), by allowing
the waste to be cleaned up on a daily basis and "socked" for a certain
period of time I would expect to leach out the most I can for the plants.
The cycles you mention about your lettuce is exactly what I want to prevent
by controlling the duration of time the waste sit in the water. I am not
planning to try to get everything out of the waste, soacking time and
temperature will be monitored carefully.
I know nothing about tilapia which I figure around 99% of everyone is using,
( am learning all the time ), I wonder if the nutrient content of tilapia
and trout waste differ greatly. As I understand the temperature of tilapia
culture is around 25C ( 78F ), trout is around 12-15C, the leaching from the
fish waste I take it is extremely influenced by this, along with the fish
itself.
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