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Re: Testing B.O.D.

On Fri, 20 Nov 1998, James Purchase wrote:


> My question is: how close an approximation of the B.O.D. can I get without
> using LaMotte's special test kit (which contains "seed capsules")

I haven't done a comparative study, but my semi-literate guess is that 
the LaMotte kit will provide higher BOD levels than you will get without 
the "seed capsules".

I've always thought that BOD would be an interesting test to make, and 
considered doing exactly what you're doing now, but somehow I never got 
around to it.  Even if your results are lower that the results you might 
get from the LaMotte kit, I think the results will be relevent to 
conditions in your aquarium.  You just won't be able to use those results 
to get a permit to discharge your aquarium water to a lake or stream, but I 
don't suppose that's what you have in mind.
> 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)?

I think your methods are about right.  0.8 ppm BOD seems pretty good to
me.  BOD is normally used on waste waters and on waters receiving
discharged wastes.  High BOD numbers indicate polluted water.  It's been a
while since I looked at a lot of BOD's but I think your 0.8 ppm would be
fairly normal for natural water.  It probably indicates that your tank has
an active aerobic bacterial culture and good circulation. 

A standard test might give a higher result than 0.8, but your results
pertain to the chemicals in your tank and the microbes that are digesting
it.  It might be hard to compare your results with standard results, but
your results are perhaps more relevant to conditions in your tank than the
standard results would be. 

Roger Miller