oxygen levels are completely independent from co2 levels. read up on partial
pressures sometime in a chemistry book for details. maybe google "partial
pressures..." i've seen lots of highschool science stuff on the web that is
pretty well written. i'm always amazed about the stuff they teach in hs now
that wasn't even known when i was in college...e.g. proton pumps...

co2 in a heavily planted tank will cause the oxygen to get to fully
saturated levels if the plants have all the proper nutrients to allow them
to produce the oxygen. the result will be the pearling that you hear about.
it will be evidenced in the extreme by a lot of bubbles (i.e. champagne
glass) coming up or in the more likely case by a lot of oxygen bubbles
clinging to the leaves of the plants.

co2 can be a problem if it gets into the mid to upper 40ppm. it's relatively
hard to do since at those concentrations it is given off more rapidly to the
atmosphere than if it is in the 20-30ppm. even at the 50ppm there could be a
saturated oxygen condition and still cause stress on the fish due to
elevated co2. that's how "unrelated" they are.

my recommendation is to feed NPK, traces and CO2 in balance with your
lighting and plant demands and don't worry unless your co2 gets to 40+ppm in
the morning. i doubt you'll get there without out extraordinary measures
with a diy system.

jtm

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