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Re: CO2 Injection Options

> Has anyone used an alternative to the very highly
> compressed cylinders for CO2 injection?
	OK, you asked...  I have a DIY Pepsi bottle fermenter connected to an
air pump distribution manifold.  The manifold feeds both a Mylar balloon
(a reservoir), and a cheap air pump.  A 556 dual timer chip connected to
a solid state relay (2 cheap Radio Shack parts) allows me to control
both the length of time the pump runs and the interval between these
bursts.  Right now the pump sends half-second bursts of gas to the
reactor every 45 seconds, which keeps my KH2 60 gallon tank at pH 6.6. 
The 556 chip can be controlled by a pH-measuring device with the
addition of a single wire.  The system is stable enough right now,
though, so I don't feel any burning need to add the additional
circuitry.  Certainly, this setup offers much better control than just
feeding directly from the fermenter into the aquarium; with our very
soft water (<1 dKH) this is a big concern.  The only maintenance
required is recharging the Pepsi bottle when the balloon starts to look
a little flat.  The air pump is connected to the timer so it's disabled
at lights out.
	I imagine the carbonic acid produced by the CO2 is going to break down
the pump diaphragm eventually, but so far (one month) so good.  A
rebuild kit is readily available and doesn't cost much. An alternative
would be to put a one square foot piece of plywood and some bricks over
the balloon and use a valve instead of the pump.  The same timer
circuitry could control the valve's "open" duration and inter-burst
interval.  This would be a very low pressure system (i.e. << 15psi),
since you'd have to place (literally) a ton of bricks on the square-foot
plywood piece. (15psi*144 sq.in. = 1 ton!)
	The idea behind this contraption was to come up with something cheaper
and simpler than the "standard" tank/regulator/valve setup.  For someone
who is comfortable with low-level electronic tinkering, it may be a
viable option.  As a bonus, the silver mylar balloon, pump, bottle,
hosing, and circuitry (complete with flashing LED, of course) sitting
next to the aquarium confirmed my lunatic status at my last Bridge
party.  The whole setup was built with hardware store and Radio Shack
parts for about $20.  My plants are growing like mad.
Sherman