[APD] Substrate Redox measurement?

["Jerry Smith" <jerrytheplater at hotmail_com>]

I was reading Tom Barr's post today where he was explaining  why vacuuming 
of the substrate is needed periodically- to remove the accumulated mulm 
which when decomposing reduces the ORP of the substrate and makes it too 
reductive. My curiosity is peaked now.

My question is: what is/are the method(s) of measuring the ORP of the 
substrate? I can envision jamming a probe into it but wouldn't this allow 
the overlying water to skew the results? What is the method used in the 
field?

I use an ORP probe while pretreating ion exchange regenerants prior to 
discharge to the POTW. It is submersible in very aggressive solutions. It 
could be inserted into a substrate but it is about 3/4 inch in diameter and 
flat bottomed. It would surely greatly disturbed the substrate and cause a 
lot of mixing of the overlying water. I guess there must be other 
configurations of these probes, just like pH probes.

I ask this question to satisfy my curiosity, not because I actually intend 
to use my probe from work to try it. It isn't portable and I can't bring the 
tank to it.

Thanks,

Jerry Smith, Bloomingdale, NJ, USA


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