Warm Yeast CO2 & Reactors

With all the recent interest in warming yeast CO2 generators and in 
powerhead injection, I just have to delurk and give back in return for 
all the great tips and techniques I have picked up here.

Two nights ago, I put my yeast CO2 setup (contained in a plastic
Rubbermaid tub) on top of the separate ballast/timer box for my DIY hood. 
The timer/ballast box sits on the floor.  When the lights are on, the
generators are slowly warmed by the waste ballast heat (now no longer
wasted :-) ).  I haven't yet measured the temperature that the yeast
bottles reach, but it is only slightly above room temperature.  Whereas in
the past, this CO2 setup would only pull my pH down to 7.1 from 7.4+ (it
would occasionally come down to 7.0 with a new yeast bottle), I have
measured 6.7 in the late day (just before the lights go out) and 6.8 in
the morning (just before the lights come on).  My alkalinity is typically
74 ppm, or about dKH=4 (LaMotte test kits for both pH and alk.), so it
seems that my CO2 concentration is 20-25 ppm, and this method seems to be
stable, so far. I am going to be watching the pH carefully, and will
report if I find that there are stability problems. 

WARNING and DISCLAIMER - the above technique places fluids above an
electrical appliance, which is not advisable unless you know what you're
doing and unless you take steps to protect from spillage!  Note the use
above of a plastic 'secondary containment' device for the CO2 equipment
(more details later); I also use a check valve in the CO2 line to my
powerhead and have shutoff valves in line with the CO2 bottles for use
when I change bottles.  If you're not comfortable with electrical stuff
and can't ensure that the electrical equipment will stay dry, don't try
this.  Also, I have just started fooling around with this setup, and am
not entirely sure that my tank conditions (pH) are completely stable. 

By the way, this is not an entirely original idea: I remember reading
somewhere either here or on the Krib about someone who had put his yeast
bottle on the ballast for his fluorescent hood, and had always meant to
try it.  Reading the recent posts about warm yeast brought it back to

I think I can already see the difference in the growth of my Bacopa
caroliniana;  I also have Ceratopteris thalictroides (spelled right?)
which was already growing like crazy under the old conditions and H.
difformis, which is still getting rooted, so I'm not expecting much from
it, yet.  The rest of my plants are too-slow growers to expect an immediate
response from (is this right?): Java fern, A. barteri nana, Crypt. lutea
(I know, shouldn't add crypts early, but at the store they said this crypt
is an exception, and besides, it was free - one of their customers had
brought it in to get rid of it). 

Now for some questions - 

Has anyone else tried this?  I am wondering about the interval of time 
after the lights go out, while the ballasts are still hot and cooling 
off.  This lag-time in the cooling of the generators will presumably lead 
to generation of CO2 when the plants are not photosynthesizing.  I 
haven't tried measuring pH at, say, an hour after the lights go out; 
maybe it dips even lower . . . the fish were still OK this morning, though.

I have just noticed in the last few days that I have some black brush 
algae growing on a piece of driftwood, and on the melted leaves of the 
crypt. lutea which remained from when it was initially planted (I do have 
several nice, new, reddish leaves on each of 3 of these plants, though).
Will the newly increased CO2 levels make this stuff better or worse?  

I just read this morning (digest #265) that SAEs will eat this black brush
stuff, and this weekend I took a printout of the Neil Frank/Liisa
Sarakontu sample AGA article on SAE's at the AGA Web site to my favorite
store.  It turns out that they had gotten a shipment of a dozen or so of
these about two weeks ago, and a single customer bought them all!  (Gotta
find out who he was, he's probably a fellow plant person...) Anyway, the
store knows where to get more and will try to do so.  The questions
(finally!): how many do I want in a 20H? 1? 2? Depends on whether
juvenille or adult? 

I already have a flying fox (Epal. kalopteris), (s)he's about 3" long, an
adult, I'd guess.  Will (s)he tolerate an SAE as a tank-mate?  The AGA
article says "agressive towards its own kind"; does this mean towards
Epal. kalopteris only, or towards all similar fish, i.e. Cros. siamensis? 
I ask because I've noticed that mine will chase all fish (barbs and
tetras) from "his"  territory, _except_ for the cory cats and oto's.  He
seems to recognize them as fellow bottom fish or fellow cat-type fish or
fellow barbel-bearers or whatever. 

More details, and tank history, if anyone is interested:

I converted a fish + plastic plants tank (20H) to moderately planted about
6 weeks ago, after I experienced a minor disaster stemming from a buildup
of crud under my UGF plate. (For some reason, I didn't go all the way and
remove the UGF, though :-(, now it will really be a big job.) By the way,
I am really grateful to Karen Randall, who gave me a lot of
help/guidance/encouragement at that point via the AGA Website Plant Tank 
Help form.

From the start of the conversion, I used DIY yeast CO2, injected through
the powerhead that runs the UGF (a Penguin 550, allegedly 145 gph).  It
seemed from all I had read here that for a 20H tank, a 1 liter bottle,
1/2t yeast (Fleishmann's), 1/2t baking soda, and 3/4 liter water would be
appropriate.  Just letting the bubbles mingle with the water by adjusting
the powerhead's flow deflector downward would only take the pH down from
about 7.4 to 7.6 (basically "full scale"  on the LaMotte comparator) to
7.1 or 7.2. 

Then I added a "reactor" by connecting a short length (3") of vinyl tubing 
(3/4" OD?) to the powerhead outlet and to a stub of 1/2" PVC pipe, which 
in turn connected via a "flush reducer" to a 3/4" PVC elbow, directed 
downward.  Into the elbow was siliconed a 1" OD clear PVC tube (as used 
for UGF uplift tubes) and, finally, on the bottom of this assembly, the 
top piece of a UGF uplift assembly (the part that usually has a puny 
carbon filter attached).  The length of the vertical section of clear PVC 
was chosen so that the UGF top-piece rested on the gravel and diverted 
the powerhead flow diagonally across the bottom of the tank.  Then I 
piled a bunch of lava rock around the flow exit so that the stream of 
bubbles would have to interact with a lot of rock surface area before it 
could escape to the surface of the tank.  The rock also hides some of the 
hardware, and my 2 baby clown loaches (~1") seem to like hide in the cracks 
between rocks.

With this reactor, my pH would drop reliably and stably to 7.1. 
Sometimes, with a new yeast bottle, I could get it to 7.0.  By the way, I
am now using 2 1-liter generators, changed alternately, to even out the
bubble rate.  I've really picked up a lot of tips like this here on this
list, which would have taken a long time to work out on my own. 

I have a DIY hood with 4 20W tubes;  the (standard magnetic) ballasts and
the timer are mounted in a separate metal box that sits on the floor.  The
ballasts are mounted at the top and warm the box so that it is warm to the
touch (somewhat, but not much, greater than body temperature).  My 2
1-liter yeast bottles, plus tubing to a 2-gang shutoff valve (to make
changing bottles easy), plus a 20-oz plastic soft drink bottle that acts
as a water seal and bubble counter (tubing from the gang-valve connects to
rigid airline tube with the end under water in the bottle, outlet tube
open end well above water level) and finally a check valve all reside in a
1-gal Rubbermaid "Rough Tote" container.  This container originally was
meant to serve as a "secondary containment" device to protect the floor
from spills, etc.  Now it serves to protect the timer/ballast.  I will
probably make an aluminum cradle, to attach to the top of the ballast box,
which will prevent the Rough Tote from slipping sideways off the box. 

This is already too long.  Thanks again for the free exchange of ideas 
made possible by this digest.

Stu Elston, in Knoxville, Tennessee, where it looks like spring may 
                                     arrive this week!