# Constant CO2 mg/l even with KH change and no pH controller?



## Laith (Sep 4, 2004)

On another forum I saw a recent discussion based on the advantages of *not* using a pH controller to control your CO2 injection but just a bubble rate. 

Posted by Jeff (magicmagmi):

"With a calibrated constant bubble rate you will always have the same amount of C02 regardless of the KH. ..."

Also a response by James (aquaverde):

"if 1 bps is fully dissolving in your tank and giving you, say, 30 ppm, it shouldn't matter what the KH reading is. If the KH shifts, then the pH will shift, but not the CO2 concentration. That’s the beauty of setting up your CO2 by your bubble rate, but I don’t see much said about it."

I can *almost* grasp this concept but just not quite!

Assume I have found a constant bubble rate (say 1bps) that keeps a constant CO2 level of 30mg/l for water with a KH of 6. If the KH falls from say 6 to 3 wouldn't I need to change the bubble rate to keep the same CO2 concentration?

I'm having a problem with understanding the shift in KH, corresponding shift in pH and a constant CO2 concentration.  

A good explanation of this phenomenon would be great! 

If the above is true, I may use my controller only as a pH monitor. My tap KH changes during the year depending on the source water used by the utility company. This way I wouldn't have to test it and/or worry about it.


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## plantbrain (Jan 23, 2004)

KH and pH are merely a relationship used to measure the CO2.

The CO2 dosing is constant.

Therefore the CO2 added into a tank should also be constant.
You could even go to 0KH and still have the CO2 rate be constant. A slight increase/decrease would move the pH easily, but the plants would still have the same relative amount of CO2 available.

I prefer setting the pH/KH/CO2 up this way personally rather than with a controller, since a controller does not measure KH.
If you forget to measure the KH after a water change or after a peroid of time, or due to substrates, driftwood etc, the KH can move and the pH generally is errored on the lower side meaning your controller and test kits measuring just pH will add *LESS CO2*.

Even if the KH is measured, with some organics, stray current etc, the pH will appear lower than the CO2/pH/KH relationship would predict...........

Hence using the pH/Kh target then adding a progressively higher dosing rate till good plant health is achieved.

This is not that hard but care must be given to fish/critters.
Since you can make the nutrients and light non limiting and the CO2 is all that's left.............

So as long as you can add it at a steady know rate(bubbles per second etc), you can easily add enough CO2 for the tank without hurting fish.

Many Asian methods go this way.
This is sort of an EI approach vs the test kit methodology which even if you hit 30ppm, sometimes many folks still have issues, even if the kits are correct...........

So then what do you do? You need another method to address the issue, this was done due to iron test kit problems.
The issue was resolved in a similar manner.

Having used algae as a bioindicator and plants also, one can look at a tank without having done any measurements and tell what is wrong.

That weens you off the test kits and uses the plants and algae as the test kit instead.

On a practical level, this is better, since we want to grow plants, not take test readings and enter data. Data alone has little meaning till it's applied.

Look for the observations first, then test to see what is means and what environmental constraints are present.

If I took test readings alone as my main reason for dosing, we would have never found PO4 additions helped so much, nor more CO2, more traces, high KNO3 etc....................

The plants are the test kit, and what we learn about here and what and why we do this hobby, it is not a "test kit" "data entry" hobby.

Regards, 
Tom Barr

www.BarrReport.com


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## shalu (Oct 1, 2004)

Laith said:


> Assume I have found a constant bubble rate (say 1bps) that keeps a constant CO2 level of 30mg/l for water with a KH of 6. If the KH falls from say 6 to 3 wouldn't I need to change the bubble rate to keep the same CO2 concentration?


There will be no CO2 change, because you are injecting the same amount of CO2. However, your ph will be lower now because kh is lower, and the same amount of CO2 produces lower ph.

Tom Barr always advocates using only ph monitor, and applying CO2 during the day only, without controller. Less chance of killing fish also.


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## plantbrain (Jan 23, 2004)

shalu said:


> Tom Barr always advocates using only ph monitor, and applying CO2 during the day only, without controller. Less chance of killing fish also.


So does Amano.
Of couse neither of us know what the heck we are doing........

Regards, 
Tom Barr


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## Laith (Sep 4, 2004)

plantbrain said:


> So does Amano.
> Of couse neither of us know what the heck we are doing........
> 
> Regards,
> Tom Barr


Of course; that's why nobody ever listens to you Tom! 

Thanks, now the concept is clearer.

But one still starts from a baseline no? So you measure KH and pH and set the bubble rate initially to maintain a pH that indicates 30-40mg/l of CO2 during peak lighting. Once that's done, the only thing you need to do is re-fill the CO2 tank when it's empty (and turn the CO2 off at lights off).

Or alternatively forget about KH and pH and just raise the bubble rate slowly over time. When fish look stressed from too high a CO2 concentration, back off until they return to normal. Then the only thing you need to do is re-fill the CO2 tank when it's empty (and turn the CO2 off at lights off).

So, how's my understanding so far?


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## shalu (Oct 1, 2004)

you got it. Or you can use the BBA test. If you got BBA still growing actively, bump CO2 up a bit. That way you probably don't need to raise the CO2 as high as fish showing stress. Works for me.


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## Edward (May 25, 2004)

Hi
The CO2 – KH – pH ratio is a nice tool but not as important and accurate as we think. 
I run aquariums under high light at zero dKH and at 3 dKH, both at the same bubble rate per second. There is no difference in plant quality. 
The KH level doesn’t seem to have effect on the CO2 viability.

The pH controllers to control CO2 injection are not helping in maintaining stable environment especially with dissolving substrates. Then we add a day - night CO2 switch and we have a rollercoaster system. 

Edward


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## Laith (Sep 4, 2004)

Edward said:


> Hi
> 
> The pH controllers to control CO2 injection are not helping in maintaining stable environment especially with dissolving substrates. Then we add a day - night CO2 switch and we have a rollercoaster system.
> 
> Edward


Are you saying that the day-night switch is not recommended at all or just not when running a controller?


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## Edward (May 25, 2004)

Hi
Where is a day - night switch in the nature? I don't think underground CO2 release just stops at sunset. Lowering pH at night due to higher CO2 level does not cause problems. In fact, lower pH is more natural like for tropical fish and plants. After rainfall the KH is almost zero and therefore the pH must go down rapidly. This is the best time for fish to breed and for plants to flourish.

I grow plants and fish successfully at pH of 4, pH of 5 and pH of 6. However not that well at high pH of 8.

A CO2 controller in my opinion is a nice tool in maintaining stable environment as long as it is being used 24/7 and at *constant KH level*. A simple bubble rate counter works perfectly well even in a *KH variable scenario*.

Thank you
Edward


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