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Re: [APD] Estimative Index for CO Dosing - Bah!

George said "Bah" but, more typical of him, gave sound, well reasoned, well expressed advice. He doesn't speak often but it's always nice to hear him.
I think the suggestions have been along the lines of fish showing signs stress being too much CO2 and not pump it up until they die. Of course, one hopes one never has to approach the latter. In this case, going under the latter will be the luckier path. ;-)
Thanks, George,
----- Original Message ----
From: gbooth at frii_com
To: aquatic-plants at actwin_com
Sent: Wednesday, March 8, 2006 11:55:56 AM
Subject: [APD] Estimative Index for CO Dosing - Bah!

I keep seeing "good" advice here about setting CO2 levels.  "Keep adding
CO2 until the fish are distressed."  I know our main focus is plants and
the fish are merely decorative elements but don't you think this treatment
is a little harsh?

If I were a newbie, I would interpret this advice along the lines of
"There is a CO2 threshold [which may be different for different fish]. If
the CO2 is less than the threshold, everything is hunky-dory. If you go
slightly above the threshold, the fish die. So stay just below the
threshold and your plants will pearl like crazy and the fish will be just

Anybody with a lick of common sense will realize that as CO2 rises, fish
will have more difficulty breathing.  Respiration is based on relative
concentrations of gases. As CO2 concentration in the water increases, CO2
will leave the blood in the gills more slowly. As O2 in the water
decreases, O2 will enter the blood via the gills more slowly.  Ever hear
of "Altitude Sickness"?  It affects different people in different ways. 
Some folks are fine on Rocky Mountain ski slopes, some people almost die.

An appropriate CO2 level is not a threshold, it's a compromise. Increasing
CO2 levels will makes the plants delirious but will affect fish more and
more.  If they are visibly distressed, it is way too high. It's like
telling a college student "It's OK to drink but only until you pass out." 
Oops, way too much.

To the Sump Guy with the fast breathing discus and pearling plants: think
about it.
A) Pearling plants -> High O2 -> Fish can inhale -> Good
B) High CO2 -> Pearling plants -> Fish can't exhale -> Bad
Hint: A and B don't cancel each other out.

My experience indicates discus are more sensitive to CO2 levels than other
fish. We would never keep CO2 above 20 ppm in a discus tank. Or any of our
planted tanks, for that matter.

20 ppm not high enough to keep algae at bay?  Do the old fashioned thing
and get some algae eaters.  Make your tank a semblance of an eco-system
rather than a large bottle of seltzer water.

20 ppm doesn't produce enough pearling?  So what?  See above.

George in Ft. Collins, CO

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