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CO2 Diffusion

While we're on the topic of CO2 diffusion, about a month ago, I finally got
around to trying something I had wanted to try for awhile.  Using duct tape,
I sealed the lid of my trickle chamber, (an old Burleson "Gulfstream" unit)
and ran the line from my CO2 regulater into the sump under the trickle
chamber.  There is a foam filter separating this from the rest of the sump,
and the "low water level" of the pump is high enough that there is no open
air area between this area and the open section of the sump, so all of the
CO2 must go into the trickle chamber.  My trickle media is standard orange
bioballs.

My reasoning was that with an abundance of CO2 gas in the trickle chamber,
it can't help but go into solution across all of that surface area.  Any CO2
outgassed remains in the chamber to be redisolved, so none goes to waste.

I've found that adjusting my CO2 flow to around 6 bubbles a second (from the
end of the tube) is sufficient to maintain a CO2 level of around 30 mg/l (pH
6.9 @ 8 dKH) in a reasonably heavily planted open topped tank with a surface
area of 13 1/2 sq. feet (160 gallons, 9' x 18" x ~18").  Dissolved oxygen
remains at saturation, even several hours after lights out.

Before my 3 year old selenoid gave up the ghost (anyone know where to get a
new selenoid for a Hamilton CO2 system?  Hamilton doesn't return my calls),
I did notice some interesting effects regulating the pH, running the CO2 at
a higher rate during the "on" phase  -- the amount of shut-off "lag" was way
higher than it was with a more conventional reactor.  When the target pH was
reached and the CO2 shut off, the pH would continue dropping for another 5
minutes or so, when it stopped virtually "instantly" with a coventional
reactor.  I'm measuring the pH from within the tank, mounted several feet
away from the trickle effluent flow (which might account for some of the
lag).  After the selenoid failed (it failed "open"), I adjusted the flow to
the current level and so far it's reasonably steady, not dropping the pH too
terribly much after lights out, but I'd still like to get back to having a
fully regulated flow; does anyone know if these are fairly universally
replacable?  Will the Aqualine Buschke unit from Pet Warehouse work on this?

So far, I like using the trickle chamber as a diffuser a lot, tho.  No muss,
no fuss, nothing in the tank to hide.

- Chuck Lawson