Aquaponics Digest - Sat 12/06/97
Message 1: Re: Re: Commercial aquaculture
from FranksFarm
Message 2: Re: Dissolved Oxygen
from Ian Beaver
Message 3: Re: Dissolved Oxygen
from "Darren J. Hanson"
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Subject: Re: Re: Commercial aquaculture
From: FranksFarm
Date: Sat, 6 Dec 1997 07:25:43 EST
Hi,
Thanks Ben, and all who replied. Good stuff here.Food for much thought!
Really appreciated it. frank
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Subject: Re: Dissolved Oxygen
From: Ian Beaver
Date: Thu, 04 Dec 1997 21:50:37 +1300
Gordon Watkins wrote:
>
> I'd like to know what DO levels folks are maintaining in your systems.
> Also how and how often you monitor and how you maintain adequate levels.
> I'm using the Lamotte titration kit which is pretty cumbersome for
> repetitive tests but is supposed to be accurate. I'd love to have a DO
> monitor but they're a little too pricey. Has anyone used the Vital Sine
> or Pinpoint DO meters?
> My levels are running around 5.25 ppm which I maintain with an
airstone
> in each 300 gallon section of my vat, and by cycling the water through
> my beds 4.5 times per day (turnover rate). I only test every week or so
> or if I suspect a problem.
> Regards, Gordon
Gordon
Are you able to be specific about the amount of air you are passing
through your airstones, ie the size of your air pump. I have been
wondering on this subject, ie how much air do you need to pump in to a
given water volume to keep the DO levels up. My observations also
suggest that not all airstones are born equal.
Ian Beaver
Northland, New Zealand
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Subject: Re: Dissolved Oxygen
From: "Darren J. Hanson"
Date: Sat, 6 Dec 1997 13:04:33 -0800 (PST)
At 09:50 PM 12/4/97 +1300, Ian Beaver wrote:
>Are you able to be specific about the amount of air you are passing
>through your airstones, ie the size of your air pump. I have been
>wondering on this subject, ie how much air do you need to pump in to a
>given water volume to keep the DO levels up. My observations also
>suggest that not all airstones are born equal.
There are a couple of things to keep in mind when attempting to design a
system to maintain a particular DO level.
Fish density - More fish will deplete the DO level requiring it to be
replaced faster.
Fish requirements - Some fish require quite high DO levels while others do
quite nicely at lower levels.
BOD from wastes - The more fish waste/uneaten food/etc being broken down,
the more DO will be consumed by bacteria.
I don't have any solid numbers for the above. My partner and I have always
used the "how do the fish look/act" test kit to determine if we're
maintaining proper water conditions. But I do know that I have read a number
of studies regarding DO requirements and BOD consumption.
After determining what you need to maintain, then you have to ask yourself
how you're going to supply it. There was mention here earlier this week
about using liquid oxygen. I've never considered using LOx for anything
other than rocket engines so I can't comment there. There are also systems
available that make us of Hydrogen Peroxide and other oxidizers in the
presence of an appropriate catalyst to produce oxygen chemically. But I
think by and large the best results will come from some sort of mechanical
agitation at all by the highest fish densities.
To this end, anything that creates a disturbance at the surface of the water
will help put O2 into the water and help drive off CO2: recirculating pumps,
fountains, or even simple airstones. The things to remember when working
with air driven methods is that the finer the bubble, the greater the
surface area but the greater the presure. Also, the deeper the airstone is
placed, the more it will cause currents to mix the water (providing even DO
levels among other things) but the greater the presure as well. However,
from my reading I have come to the conclusion that 99% of the air exchange
occurrs at the surface of the water, almost no air exchange takes place at
the surface of the bubbles due to surface tension.
Currently my partner and I are using a 3/4 hp blower to supply air to around
100 tanks of various sizes for use in producing ornamental tropical fish.
These tanks vary in depth from approximately one foot to nearly three feet
in depth. The larger tanks have multiple airlines to provide enough
circulation and surface agitation. And while we use various methods to hold
the airline under water (from simple lead anchors to sponge filters) we
restrict the airline an absolute minimum. This provides a maximum volume of
air to create currents and disturb the surface where the true air exchange
is taking place.
Just my two cents worth.
-- dj
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