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Re: Aquatic Plants Digest V3 #76

John (or is it Dave?) McKenzie said, Sunday, Feb. 8:

>I have a 125g tank with moderate light levels CO2 injection and 7.0 pH.
>I use PMDD .  When I make my weekly 25% water change the plants put out
>O2 like crazy for one day.  Then they return to rather unspectacular
>growth.  The plants are rotala i., ludwiga r., swords and a few misc.  I
>live near Chicago and use tap H2O for changes.   My tank nitrates are
>5ppm and PO4 is 0.2 ppm.  I'd like to have O2 coming off m plants
>throughout the photoperiod.  Any advice?

If you add water directly from the tap when you do your water change, that
bubbling from your plants may not be all O2.  Tap water has been under
pressure, and when returned to normal (1 atmosphere) pressure, is
supersaturated with nitrogen and oxygen.  These gasses come out of
solution, some into the atmosphere from the water surface, some into little
bubbles that form on the plants and glass, and some into the air channels
of the plants, causing them to bubble more.

Paul Krombholz, in central Mississippi where we are actually drying out a