CO2: To Inject or not to Inject

T

TerenceBoyle

AC Members
Sep 21, 2007
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Ok, I have finally gotten to a point where I understand my water chemistry enough to ask this question. It is:

PH: 7.4
KH: 19-20
GH: 11-12 (irrevelant for this question)

(This is after it sits for a couple of hours... it initially comes out of the tap with very high CO2 resulting in a PH measurement of 6.7-ish once the CO2 disappates the above numbers are evident)

This puts my CO2 levels at 23 ppm... right at the high end of acceptable range.... OK good, so I can use my tap water... even for changed (provided I let it 'age' for a few hours and don't kill the fish with a huge quantitiy of CO2).

Do I have it right so far??


Assuming I do here is the real question / next step:

I am using 130 watts of lights w/ ferts on a 30" long x 24" high x 12" wide. I plan on using the high light to grow some really interesting plants in a moderately dense set up. Most of them require high light (got it)... most say they require CO2... given my numbers do I need to inject CO2 or will it just puish the levels over the top?

I am guessing that I should get the injector along with a PH monitor (I like automation) because as the plants use it... the PH will down... the system will come on... the ph will come back up... they system will go off and so. In other word it will keep my CO2 and PH levels right where I want them (which is probably right near the starting point so I can do those water changes without worry about throwing things off).

Help... please.... thanks.
 
Any co2 in your tap water will be used immediately in a high light, densely planted tank. You will need co2 injection. Ph shift from co2 levels alone, will not hurt your fish. My tap water is 7.8, my tank ph is 6.4. Part of the ph is from my driftwood, and part from my co2. My co2 runs for 24 hours a day, with practically no ph change.
 
CO2 in non-injected water is around 5ppm so the pH/kH chart is not accurate in your case, the pH/kH chart can be inaccurate if there are other buffers or acids in the water. You're going to need CO2 going with high light, invest in a drop checker and use water with a 4dkH for a more accurate CO2 measurement.
 
OK. I get the part about buffers screwing up the chart, but help me out with:

- drop checker?
- 4dKH?

Thanks
 
Yes, that's a drop checker, they have fancier glass ones on eBay for not much more but they all work the same. It's basically a container that hold a diluted bromothymol blue solution with an air bubble separating the solution from the tank water. CO2 can transfer through the air bubble so it affects the solution causing it to change color. Nothing else can affect the solution so it's much more accurate than just the pH/kH chart.

The diluted bromothymol blue solution should be mixed with water with a kH of 4, where approximately 30ppm of CO2 will change the solution from blue to green.

I don't use a pH controller so I don't know how they set up. For an automated system I just use a solenoid attached to timer. Set up the bubble rate for 1-3 bubbles per second and then wait a few hours for the drop checker to to work, then tinker with the bubble rate until it turns green. Then set the timer for the solenoid to go on and off before or at the same time your lights go on and off.

For the longest time I also ran my CO2 24/7.
 
Thanks. I think I'm on the right track.... for now anyway. I'll check back in once the equipment comes in and the tank starts coming together.
 
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