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Re: Aquatic Plants Digest V4 #27

Hi all,

Of course it's true that CO2 and O2 levels are completely independent in the
water. However:

it's CO2 vs. O2 levels in blood, not water, that matter. While CO2 and O2
levels are independent in the water, they are NOT independent in blood,
where hemoglobin's higher affinity for CO2 causes it to displace O2.
in an inadequately buffered tank, CO2 induced declines in pH induce declines
in blood pH, which (further) reduces hemoglobin's O2-carrying capacity
the practice of minimizing surface agitation to avoid CO2 loss, while
independent of CO2 itself, has a significant effect on lowering dissolved
oxygen, other things being equal. Lack of current-induced water movement
across the gills also reduces blood O2.
plants oxygenate the tank only while photosynthesizing. Depending on the
vigorousness of plant growth and fish stocking levels, accumulated O2 may
not last the night. Especially in the case of those just starting out with
planted tanks, fish stocking levels are likely to be high and plant growth
weak (and buffering capacity too low).

Seen from another angle, a lot depends on the kind of fish you have. Fish
adapted to breathing O2 from the surface will do fine in spite of
everything, whereas rheophillic (current-loving) fish are not good
candidates for still, planted aquaria, even when dissolved O2 is high.