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One problem with media beds is that they need to be taken out of service to clean. If a person could identity bed zones that were trending toward becoming anaerobic and perform “targeted” cleaning, the bed could stay in service with minimal harm done to the biofilm.

One way to perform such trending is to profile the solids layer with an ORP probe on a monthly basis and record and chart the results in a spreadsheet.

The following illustration can be used as a guide for interpreting the results.

schematic presentation of flooded soil from Y.Chen and Y Avnimelech

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Terry, have you used an ORP probe to check on the condition of a media bed? I have never used an ORP probe and don't understand how to sample selected depths in the media bed.

Wow Terri, this is cool stuff (I'm still not sure about how exactly one would go about selectively cleaning the bottom-is layers of a grow bed though).

Pices, it's basically just a millivolt meter that measures an electrical current across a reference electrode and a measuring electrode. For basic AP purposes you could look at it as measuring oxidizers (oxidants = good) and ruducers (reductants = bad...ALTHOUGH, the Fe3+ reduction zone would be prime real-estate in which to bury some old rusty nails for conversion to plant usable Fe2+...IMO).

The reading in millivolts can tell you if things are aerobic, anoxic, or have gone full blown anaerobic. Notice that as the O2 levels decrease, so does the reading in millivolts...from positive to negative.

As far as how...That's better left to Terri...but I imagine you pretty much just stick the stick-like probe into your GB at a given depth and just read what the display portion says...

Terri, how do you go about "target" cleaning your GB without disturbing the bio-film? This sounds intriguing...

Thanks Vlad, other than sampling a media bed for anaerobic tendencies, is an ORP reading useful for maintaining an optimized AP system?

Useful...sure. I'm a sucker for cool probes, meters, (relatively) precise measurements of data which is "useful" to me in varying degrees and in various ways...even if it's just to fulfill my curiosity about something, or to test out an idea. Much of this might not be absolutely necessary, but certainly still useful.

Once we start getting into "optimized" (to use your terminology) scenarios, then the more data you have, the better off you are with being able to implement your methods/strategies for 'optimization'. 

I've never used an ORP in a home aquarium, or any bio-ponic system, and personally feel that anoxic zones have their place (within reason, of course) in these type of systems, for certain redox reactions. It would be nice to be able to track them somewhat. I probably would use one (ORP) in a different way (to acheive different ends) than an operator who feels anoxic zones should be eliminated entirely from a system...all useful stuff, if not entirely necessary.


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