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Re: QYNGA - ORP levels for Freshwater Planted Tanks
On Wed, 19 Nov 1997 09:28:52 -0700, George Booth
<booth at hpmtlgb1_lvld.hp.com> said:
>One of my QYNGA was "What's the correct ORP level for a freshwater plant
tank?" No one
>on rec.aquaria ever answered it so I stopped reading that group.
It's nice to be able to try to answer one of George's questions. The
following information comes from"Limnology", 2nd Ed, Horne & Goldman
published by McGraw-Hill 1994:
"...at neutral pH and 25 deg C, oxygenated lake water has a redox
potential of about +500mV. Under these conditions most common metals and
nutrients are thermodynamically stable in their most oxidised forms. Iron
will be present as Fe3+ (ferric iron), not Fe2+ (ferrous iron).
Similarly, nitrate rather than nitrite or ammonia will be present, and
sulfate will be more stable than sulfide."
Other comments made are that as the redox potential falls, ammonia
becomes favoured over nitrate between +450 and +300 mV ( a later comment
says at less than +350 mV), and Fe2+ over Fe3+ at between +300 and +200
Does +500 mV sound like a reasonable ball park figure to aim for? I hope
so because I'd hate for you to stop reading this list <g>.