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[APD] Using the estimative index for CO2 determination and problems with measuring CO2

Someone asked on another forum about the problems measuring their CO2 with
peat or other potential acids that would interfere with CO2 readings.
It dawned on me that I did something similar as I did with the nutrients
and lighting. 

About CO2: 
I do not pay much heed to keeping the CO2 at a certain set range based on
pH/KH readings if things just don't look right in the tank. 
This sometimes means the CO2 is not what the test might indicate due to
other acids etc that depress the pH giving a lower actual CO2 ppm.

It's seldom ever the case that buffer will push the pH up and give a higher
CO2 ppm reading.  
I'll double check the test etc and if I'm still not satisfied, I'll add
more CO2 anyway.

If the CO2 measurement is going to be off...................it's going to
have less CO2, not more as a general rule. So I'll add a little bit more
incrementally. Until I see the plant growth I know I should have and no
signs of fish CO2 stress.  

The approach is similar to finding optimal Traces levels which are
difficult to test for. This gets around poor test kits and focuses on the
plants themselves. Some kits are just unable to tell you what you need to
This occurs with CO2 also sometimes.  

Get the rest of the parameters in good ranges, then isolate the variable of

As long as you have a way of adding a known steady amount(Rate), you can
find the CO2 injection amount you need. 
I believe this is why many folks in Asia and Amano use bubble rates, they
work with this method as long as you add a steady amount.
But many did not carefully measure the CO2 also for some reason. Doing both
is a good method IMO.

Keep adding more till you no long get a good plant response. With CO2, this
is fairly easy. 

I suggested 20-30ppm for plants some time ago by doing this. I'm leary to
suggest others try this without a careful eye, good steady delivery of CO2,
turn your CO2 off at night(reduces any errors or build up that might occur
with a 24/7 routine). 

Years later(2003) I found a reference by Bowes on photosynthetic
characteristics (CO2 and light saturation maximums) that showned 30ppm as
the maximum amount that will help plants.I came to this amount by doing the
above method when I used higher light. 

The "off at night routine for CO2" is similar to the notion I use for
dosing of the nutrients(Estimative index). 

With the KNO3 etc .....you add a bunch and then do a large water change to
remove it all to prevent excess build up. This gives you a good range
that's fairly easy to maintain.

But with ____gases___, the off gassing at night provides this prevention of
build up of ___excesses__. So no water changes are needed to achieve the
same result on a daily basis with gases. 

Instead of re setting the tank each week with a water change, you let the
CO2 outgas.
Amano does the same thing. Cranks the CO2 in there, then shuts it off at

Screw the "pH stability is better" idea. I've never found that to have
merit and I've been doing this for over a decade with all these so called
wimpy fish. 
What happens when we do a 50-70% water change with tap water? pH changes
are huge. Fish love it. 

Yes, you can still get 30ppm using 24/7 CO2 dosing methods and have a nice
tank. But if something interfers with the pH, you can have less CO2 than
you think. 
Plants are still the best indicator.  

By isolating the parameter of interest, you get a much better idea of what
is going on and how to get around poor testing procedures or things/results
that just don't add up. 

This is what helped me figure many things out were many other folks had
problems in the past. 
So isolate the issue first and get the other nutrients and light in line
with what you want, then vary the rate of the CO2 slowly, use off at night
to prevent less build up and a peroid of offgassing to remove any excess.
Plants do not use CO2 at night and it's not needed then. We add CO2 for the
plants, not pH control directly.  

CO2 is a bit tougher due to high levels causing fish issue but still to
this day, I've never killed a fish with CO2 gas. 
There's also another way to arrive at a close approximation of CO2 with
peat.......but I posted a method in another post in the past here

Tom Barr

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