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Re: Aquatic Plants Digest V3 #1307

> The other question is, where is my CO2 going? I have one bubble per 
> second coming through an Eheim diffuser, which in turn is right below
> my Fluval intake. As far as I can see *every* bubble is being
> dissolved. This should really be more than enough CO2 for a 29 gal
> tank, right?

Seems like it should be, but apparently this bubble count thing
is less than imperical. :D  The number of bubbles required
depends on bubble size, diffusion method, surface turbulance and
water movement, plant quantity and metabolic rates, light
intensity, temperature, and probably several other factors.

> But my pH only changes from approximately 7.8 to 7.6. By the chart,
> that gives me between 4-6 ppm CO2. Shouldn't I have more than that?
> There is little to no surface agitation.

There can be a big difference betweeen "little" and "no" surface
agitation. I recently reduced the turbulance in my tank from
what I considered "a little" to "almost none" by modifying the
return diffusor and experienced dramatic increase in CO2
content. It went from between 15 and 25 ppm to around 50 ppm
(over a 2 day period), even though I was reducing bubble rate,
from this very slight change..

> Should I crank up the CO2 and try for a significant pH change?

Yeah, I'd go ahead and get the pH down to where it needs to be
to have 5-15 ppm of CO2 based on the KH, then let it stabilize,
then look for ways to make the CO2 injection more efficient.

> Or does an alkalinity of 7-8 dKH really make it hard to change the pH
> with CO2?

I wouldn't think so, but if possible, lower it to 5 or 6. Mine's
at 6 and I go from a pH of 7.8 to 6.8 with 30 bubbles/minute in
a 45 gallon tank.

> From the chart, it seems like bringing the pH down to 7.0 with CO2
> would give me a nice 20 ppm, but I'm curious just how much CO2 that
> would take.

Because there are so many variables from tank to tank, there's
no way to predict it accurately. If one bubble/sec is only
dropping you to 7.6, try two bubbles and see where it goes. If
that's still not enough keep increasing bubble rate until you
get to 6.8.

I think somewhere you are losing CO2 somewhere, because 1
bubble/sec probably should move the pH on down to below 7.0 in
your 29 gal, even with a KH of 8.

When you put food on the surface, does it move or stay right
where it falls?  What kind of return is there from the filter?
Is the filter open? (Sorry, I'm not familiar with Fluval

Dan Dixon