[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

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>.

David Aiken