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VHO's and CO2 reactor design

> From: "Michael A. Bateman" <spine at stlnet_com>
> 
> > The rule with HO's and VHO's is that they put out 2x and 3x more light,
> > and they burn out 2x and 3x faster, respectively.  In theory, you'd have
> > to change your VHO's every 2 months (that is, if you're a die-hard plant
> > fanatic who'd change their NO bulbs every 6 months, unlike the rest of us
> > droogs who just wait until something burns out in one of the other tanks
> > before swapping tubes and buying new ones).
> 
> Eric, this is not necessarily correct.  I think the key is what type of
> ballast is used with the bulbs.  My set up uses the IceCap electronic
> ballast.  In this configuration I've had my VHO Aquasuns running 10-11
> hours a day for well over a year without failure.  This weekend I did
> replaced all four lamps because my plant growth had slowed.  I see no
> reason why anyone would need to replace a VHO bulb but once a year and I
> know others who have also indicated the same experience.

But.... How long will you be able to run a NO with an Icecap ballast?
Could you perhaps run one for.... THREE years maybe?  If you use a better
ballast, it will improve ANY bulb.  Personally, I keep my NO bulbs for 2
or more years, because I'm not THAT critical of having super optimized
light level.  So I stand by my original statement that you need to replace
VHO bulbs 3 times more often than NO bulbs.

> From: Jim Curto <jkcurto at tensornet_com>

> I agree with your thinking on having the powerhead push water in through
> the top of the reactor tube and exit through a hole in the side just
> above the gravel and also to have the gas tube from the generator come
> in through the top. I built my reactors your way. Thanks. I do not have
> anything in the lift tubes I'm using. Would you repeat the logic on
> using media in the reactor?

If you leave the reactor empty, then the surface for CO2 exchange with the
water is limited to the pool of water halfway up the reactor and possibly
the side walls if the water does not inject right into the center (or
alternatively, at the tiny surface of the stream of water free-falling
down the tube). If you trickle the water down some form of media, then gas
can be exchanged at the surface of the media, in exactly the same way
bacteria get at the water in a trickle filter.  The media under water is
useless when you inject the CO2 from the top -- a friend of mine uses
rocks for that part and bioballs above the water line to save a bit of
money.

I have shifted design a couple times.  Initially I built a reactor the
same way I do now, with both water and gas injected from the top.  Some
folks here suggested I inject the CO2 from the bottom, as it could then
trickle "up" through the submerged media, wheras CO2 from the top just
"stays there" like the inverted bell designs.  What I learned was that
when you inject CO2 in the bottom, it gets pushed right back out through
the nearby water exit hole!  I changed that design shortly after. 

(The original 1994 design can be seen at
http://www.cco.caltech.edu/~aquaria/Krib/Plants/CO2/reactor.html for
comparative purposes.  My new reactor is basically the same sort of unit,
except that the CO2 comes in at the top and the water exits at the very
bottom.) 

And since I'm at it, the other important factor in CO2 reactor design I've
seen is water flow.  It should not be too slow!  Gotta give lots of
chances for the gas to mix with the tricking water.  I had lousy luck
until turning up the flow rate.

  - Erik

---
Erik Olson				
eriko at wrq_com