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Unanswered CO2 question

A day or two ago someone asked about a report he'd read that CO2 is best
injected through a reverse UGF.  No one answered, so I thought I'd give my two
siamensis.  I have messed with RUGFs some and can offer some observations.

Most folks on this list (operative word-MOST) prefer not to use UGFs, whether
conventional or backwards. They do have some advantages, and here's one I
hadn't thought of.  By sending the CO2 down under the substrate, it would
maximize the opportunity for the CO2 to be dissolved into the water.

Reverse flow can also offer a couple other advantages:
1)  On George Booth's website, he lists the advantages of substrate heaters.
On the list is the idea that plants can benefit from "warm feet".  Pumping
heated water down under the plate and letting it rise through the gravel can
achieve this.
2)  RUGFs, particularly air-driven ones will provide a current through the
tank without causing CO2-depleting turbulence at the surface.
3)  RUGFs can help keep the upper substrate clean by gently pushing detritus
and other stuff back up for removal by the intake end of the filter, or by a
second cannister or power filter.
4)  I just removed an air-driven RUGF from a thirty-gallon tank.  I was taking
the tank apart to improve its substrate.  When I pulled the tank away from the
wall where it had been sitting for several months, I noticed stains which
appear to be DOCs which the air bubbles adsorbed on their way through the up
tube and then "atomized" when those bubbles popped.  I pulled the filter out
so I can experiment with this serendipitous idea after I finish my 55 gallon
project, growth of which has currently reached a CaSh limited state.  But an
idea worth messing with, even if it takes out only a limited amount of

There are a number of effective ways to get the CO2 to diffuse into the water
before the bubbles escape to the atmosphere.  I suspect this may be the most
effective I have heard of, considering the amount of time the bubbles would be
compelled to spend submerged.  I wouldn't recommend everyone ripping up their
tanks just to get the advantage this would offer.  And each of us should be
free to make individual decisions about their filtration, or even their lack
thereof.  But if you are designing your next tank and want to try this, what
the heck.  Go for it.

Bob Dixon