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Re: Low oxygen vs. high CO2
As you may recall, I had reported that after performing a major
pruning in a tank with minimal surface agitation, I woke the next
morning to find 3 (of 3) dead SAEs and 1 (of 4) dead clown loach.
Other fish were suffering, but all recovered quickly when aeration
was added. I did not connect the pruning and the deaths until
a while later when I pruned again and found my 3 replacement SAEs
suffering severely while other fish were gasping at the surface.
Again, aeration provided quick relief.
I theorized that this was due to a low oxygen condition caused by
increased plant metabolism when repairing the damage caused by
pruning. I do not believe that this was high CO2, since it occurred
at night while the plants would not be absorbing CO2 anyway.
I remember reading once that pruning large amounts of macro algae such
as caluerpa (sp?) in reef aquaria causes a similar problem due to the
release of large amounts of the fluids contained within the stems.
Apparently the fluids cause a rapid drop in the redox potential of the
Maybe this is a similar effect. The plants aren't consuming the oxygen,
the fluids are "polluting" the tank and lowering the redox potential.