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Re: testing BOD

> Date: Fri, 20 Nov 1998 14:29:39 -0500
> From: "James Purchase" <jpurch at interlog_com>
> Subject: Testing B.O.D.
> A question for the Chemists....
> If I measure the D.O. in an aquarium on Day 1 and then take another sample
> and keep it in the dark at 20C for 5 days and then measure the D.O. in that
> sample on Day 5? 

Alright James, I'll take a stab at it. First, to keep the D.O. from 
being lost to the atmosphere, the samples need to be covered, with no 
airspace if possible. Fill it to the rim, just remove all the air, as 
to not to provide more O2 or to give the sample a chance to lose it 

>Is there something special in the "seed capsules" that are used in 
>the B.O.D. kit or would the organics and bacteria naturally in the 
>aquarium water be sufficient to provide at least a ballpark figure 
>for B.O.D. in the tank?

The seed is actually bacteria cultivated for use in treatment plants, 
etc. It's just bacteria, so your aquarium should have enough present 
to give you a ballpark figure. The nutrients in your water also 
should be enough to keep the bacteria active.
> Last Sunday, the D.O. level in one of my tanks was measured at 7.0 ppm O2. I
> took another water sample and kept it in the dark at 20C for 5 days. Today
> (Day 5), I measured the D.O. in that sample and recorded the D.O. at 6.2 ppm
> O2. Am I correct in assuming that the B.O.D. in the aquarium is 0.8 ppm O2?
> If this is an accurate measurement of the B.O.D., how would this rate as an
> indicator of the health of the aquarium (the 0.8 ppm reading)?
Sounds pretty healthy. That means there was only enough bacteria and 
nutrients to use 0.8ppm of your available O2. Stuff like wastewaters 
and even badly neglected aquariums (things other people have ;-)), 
will gobble up the O2, letting you know this stuff isn't clean and it 
will use the O2 needed by living organisms. Hoped that helped.

Jamie Johnson         "Keep your eyes on the stars
Chemist-Trace Metals   and your feet on the ground"
Davis & Floyd, Inc.            -Theodore Roosevelt 
jjohnson at davisfloyd_com