Re : How to maintain high PH/KH with CO2 injection

[Roy Cheok <roycheok at cyberway_com.sg>]

Hi George

Thanks for taking the time to respond personally. I really appreciate it. 
I guess the recent discussions on PH, KH, CO2 and O2 equilibrum have 
sharpened your skills.....heheh :)

>Not really. Even with a KH of 10, the "bare minimum" CO2 level of 10 mg/l
will 
>still give you a pH of about 7.5.  You would be better off looking for
plants 
>that don't require high CO2 levels and settle for slow growing "decorations" 
>rather than a "real" plant tank.  Anubias are a good choice. 

Yes...I've pondered over this....but I really want to have a 'planted' tank. 
Maybe not quite Amano style of course....but with Echinodorus sp, 
(I have about 10 plantlets of E. Ozelot 'red-flame' on 3 separate stalks),
crypts, Java Ferns. You are right...these are probably not the CO2 hungry 
plants around.  You see...I have 2 full fledge planted tanks....and will be
using 
the excess cuttings in the African cichlid tank.

Okay....after your msg below...I think I have the right understanding of the 
KH/PH/CO2 table now. Thanks for clearing it up. I had the ealier
misinterpretation
that you use the PH and KH levels to determine what the CO2 concentration
is in the 
tank...but I now see the flaw...it does not take into consideration the CO2
bubble rate.

Now, I'm not sure if the fish can really tolerate a lower PH....but I guess
anything 
above 7 should be acceptable, also the books generally publish 8 - 8.5 PH.
Yes, 
I think the KH and probably GH is more important to the fish....

So...if I target the PH to be 7.4 for example and to maintain the CO2 at 20
mg/L...
I'll just have to adjust the KH to correctly buffer the water....and then
fine-tune 
the co2 bubble rate....right????...and referring to the table....I need a
KH of 
between 15-20 dKH. 

Hmm...now if I wanted a PH of 8.0, and referring to the tables again....looks 
like it's impossible...unless my KH is somewhere above 60-80 dKH....Now is
this 
correct. Does this mean that the available KH that buffering the water will
sort of 
'neutralize' the dissolved CO2...and thus at higher PH levels.....it is
difficult to 
main high CO2 levels without having elevated KH...otherwise the PH will
crash!!!

Also, what do you think of the other person's idea on APD....to built some
sort of 
CA-reactor based on the CA-reactor that's used in reef tanks to maintain 
alkalinity and calcium levels. Can this work to increase the CO2 levels as
well????

thanks and rgds,
Roy Cheok
Singapore


>BTW, do the fish *really* require a high pH or can they deal with any pH
as long 
>as the KH (alkalinity) is high?  Typically, the pH is not a factor but just 
>happens to be high in their environment due to the high alkalinity.  For 
>instance, discus do well at any pH as long as the GH (calcium hardness) is
low.  
>The question may be hard to answer, since high alkalinity usually creates
high 
>pH and perhaps no one has tried a lower pH with the fish. 
>
>>Obviously the injected CO2 will tend to lower the PH and KH...etc,
>
>Please do further reading on the pH/KH/CO2 relationship. CO2 has nothing
to do 
>with lowering or raising KH. This seems to be a common misconception.
>
>KH and CO2 are both independent variables - you, the aquarist, set the KH
level 
>(by adding sodium bicarbonate or calcium carbonate, for example) and set
the CO2 
>level with the injector. The amount KH and CO2 then determine the pH.
Changing 
>the amount of CO2 changes the pH only, not the KH. Changing the amount of KH 
>changes the pH only, not the amount of CO2. If you try to change the pH by 
>adding some of the pH adjusting products, you are messing with the
alkalinity 
>such that the pH/KH/CO2 table is no longer valid and you don't really know
what 
>you have.   
>
>In practice, one usually decides how much CO2 is desired (for example, 15
mg/l) 
>and what pH is desired (for example, 7.0). From a pH/KH/CO2 table or
chart, one 
>then determines that a KH of 5 degrees will give a pH of 7.0 with 15 mg/l of 
>CO2. 
>
>The aquarist then adds enough carbonate of some form to achieve 5 dKH. This 
>causes the pH to rise to some level above what is desired. Then the aquarist 
>adjusts the CO2 injector until the pH comes down to 7.0. [Note that the
aquarist 
>does NOT simply set the injector to "n" bubbles per second except perhaps
as a 
>starting point]. The goal is to arrive at the desired pH, giving the
desired CO2 
>with the selected KH. 
>
>Regards,
>George Booth
>

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