(top-posting repaired...)

"jd" wrote in
:
"atomweaver" wrote in message
I'm not big on fluid dynamics, but it seems totally plausible to me
that JD
was holding such a bubble in a static location (a "dead" corner?)
under the
UGF with the flow from his air pump, and the failure of the pump is
what allowed it to diffuse into the tank. The rapidity with which
his water quality dropped (2 days, IIRC) indicates more than just
normal metabolic action of some fish in a heavily planted tank. JD's
story may actually be another indictment of UG filters, as that rapid
drop in water quality might
not have occurred if the UGF wasn't there, but I guess not enough is
known to say for sure.


I have to disagree. With glass bottom tanks, it is very easy to see
what is going on under the UGF. There are no air bubbles. The air
stones are located abotu an inch above the bottom of the lift tubes,
so there isn't any way for air to get under there anyway...
-JD


*shrug* Perhaps a UGF dead spot holds the toxics dissolved in water, then.
My own experience with UGFs is limited, and had poor results compared to
modern options.... But, people used UGFs for decades, and they kept FW
tanks just fine. It seems you can make UGFs work for you. Good on ya',
then. HOBs and cannisters are IME much easier, safer and effective, but if
you've got something that works, too, keep at it. Still, a big water swing
in two days with an active operating cannister filter is an indication that
something more was going on in your tank. Big die-off in the UGF bacterial
colony itself, maybe? Once you stop flowing water in the UGF, that
underplate area could go anaerobic pretty quickly, kill off your bacteria
colony, and then diffuse into the tank from there. (another) *shrug*...
like I said, not enough known to say for sure.

DaveZ