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Re: CO2 dumping simulation & PMDD recipe

George wrote:
> >Date: Tue, 19 Dec 2000 16:11:17 -0800
> >From: Dave Gomberg <gomberg at wcf_com>
> >You can pretty clearly see the dump
> My lord, Dave, put a darn needle valve on the system and get over it.
> >This again underscores the importance of having a strategy to deal with
> >dumping.
> Is anyboby else shaking their heads at the relative nonsense of this all?

I have to side with George on this point. To those familiar with the
engineering principles of flow, this is pretty basic stuff but I can
understand and sympathize with the rest of the folks who are just plain
confused by all the techno-babble.

A regulator and needle valve are an excellent combination for achieving
the low and consistent flow rates of CO2 that we want. Add a diffuser or
reactor of most of the designs mentioned in the APD archives and it
should work well. I use a powerhead and inject the CO2 directly into the
air port of the powerhead outlet. Most folks put the tube into the inlet
but that's not essential at all. The special reaction chambers probably
add an order of magnitude efficiency in dissolving the gas but you need
very precise control to tune it well enough to achieve any economy. Add
a pH controlled regulator to achieve a more constant pH level or to
achieve consistent optimally high concentrations if you must have high
growth (note other factors may be more dominant). I think you can get
good growth rates with low concentrations attained with 1 bubble every 4
to 10 seconds. Its no big deal especially with a cylinder of CO2 gas vs

As for what's the right PMDD recipe:

I don't think its going to make a big difference to growth rates if you
just ensure a regular supply of those nutrients. You can probably save a
few pennies on Epsom salts by going with the latter recipe. Mg should
not be in larger concentration than the Ca I've heard. 2:1 molar ratio
is about right. High Mg tends to interfere with Ca uptake I recall. The
amount of nitrogen added depends upon whether the tank is mature enough
to handle an N bump and if there is an abundance of phosphate and the
tank is primarily N limited. Small (regular) doses of N are preferable
and fish food is often sufficient but not always.

In summary: plants are that fussy about the precise ratios of nutrients
and grow well when all requirements are sufficient.
Steve Pushak                              Vancouver, BC, CANADA 

Visit "Steve's Aquatic Page"      http://home.infinet.net/teban/
 for LOTS of pics, tips and links for aquatic gardening!!!