Confusion on CO2 (the Hoppy and Chuck quandry) - The Planted Tank Forum
 
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post #1 of 7 (permalink) Old 04-11-2006, 08:26 PM Thread Starter
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Confusion on CO2 (the Hoppy and Chuck quandry)

I'm sure I am missing a simple explanation for this...and if so...please just direct me to the thread for the answer.

Tank water parameters:
pH 7.4 (hand-held probe)
gh 140 ppm (7.84 degrees)
kH 100 (5.6 degrees)
2 DIY yeast bottles on a ladder.

When I let the tank water sample stabilize over 24hrs, I get 8.4 or so ph.

According to the first chart, it appears I am getting around 6-7ppm CO2.
https://www.plantedtank.net/forums/at...f?d=1107560221

According to the second one, with a stabilized increase of 1.0, I would be getting around 40ppm CO2.



That seems like a large delta.

I call it the Hoppy/Chuck quandry since I've seen the one chart on Chuck's site...and Hoppy is talking about the other one quite often.

Last edited by Bombay; 04-12-2006 at 01:05 AM. Reason: add info
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post #2 of 7 (permalink) Old 04-11-2006, 11:06 PM
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Couple of things that seem wrong:

A kH of 100 ppm does not equal 10 degrees. That's more like 5.6 degrees.

If your kH is 5.6 degrees, then the equilibrium should be around 7.8, not 8.4.

If your kH is 5.6 degrees, then pH 7.4 would mean about 6.5 ppm CO2 in your water, which isn't much over equilibrium.

You need to do some more double-checking. Maybe there is something in your tank (decorations or substrate or additives) that throws off the Chuck/Hoppy equation. Boy that sounds scientific.


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post #3 of 7 (permalink) Old 04-12-2006, 12:11 AM Thread Starter
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Wasserpest, yeah, I needed to multiple by 0.056 to get degrees. Fixed that above. The delta still remains.

According to Chuck's calc, that give me around 6-7ppm...which is what I started with basically. Since the initial calc, I added another hagen bottle which boosted the bubble count from about 6 to around 16-18 bpm. My plants are growing and shooting off streams of bubbles.

About the equilibrium. The water in my tank is not tap water, but partial water from an existing tank plus RO/DI bottled water. I've tested the ph and kh over the past couple weeks and haven't really seen a change. The ph did go down .2, and has held steady at around 7.4ish. The last time I measured a sample straight from the tank it was 7.41...and after 24 hr it was 8.47. Accordingly, it seems, that 1 point should give me 40ppm CO2.

I have some driftwood, eco-complete, and plants.

Need help.
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post #4 of 7 (permalink) Old 04-12-2006, 02:16 AM
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I don't us a PH probe, but I have read here and other places that those probes are not accurate if used near a operating light fixture, heater, powerhead, etc. They are sensitive to electrical interferrence. I suggest turning off every electrical device within four feet of the tank before using the probe to measure PH. Other than that I have no idea what is going wrong!!

Hoppy
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post #5 of 7 (permalink) Old 04-12-2006, 02:38 AM Thread Starter
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Quote:
Originally Posted by Hoppy
They are sensitive to electrical interferrence.
Hey Hoppy, as per the probe instructions, I take a sample of the water and then test it. Come on veterans, don't abandon me now!
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post #6 of 7 (permalink) Old 04-12-2006, 03:51 AM
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You may be mis-measuring the KH. The PH drop test doesn't assume anything about KH except that the two samples have the same KH. I find it pretty easy to get KH accurately with the titration test that Aquarium Pharmaceuticals sells, but it is more accurate if you double the water sample size and divide the number of drops it takes for the color change to occur by two. Your test is different, obviously, and may not have as sharp a delineation between colors. I have that problem measuring PH. Some kits can work well in a limited range, but not be accurate outside of that range. These are just thoughts you might consider. And, in my opinion, you had about 40 ppm of CO2 when you did those measurements in the original post.

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post #7 of 7 (permalink) Old 04-12-2006, 02:39 PM Thread Starter
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Quote:
Originally Posted by Hoppy
And, in my opinion, you had about 40 ppm of CO2 when you did those measurements in the original post.
Not sure what you mean by that Hoppy...assuming you are talking about this post above.

I used to use the API tests but mine were getting old so I switched (don't know exactly why) to Hagen. In reading the booklet (again) last night, if I recall correctly, they also utilize the titration method. I am willing to try anything to figure this thing out (how much CO2). I will try the doubling method. With that said, continued tests give me the same results.

I'm doing some additional experimentation with two tanks: the new planted 20 and a 7 year old fish only (lowly stocked) 46 gallon (no plants, no co2). One of the things I am trying to track is the difference in ph fluctation between night and day. By using the fish only tank as a constant, I hope to understand what I may be subjecting my fish to in the way of fluctuating pH.

Measuring pH at:
morning (new sample at 6:30am)
early evening (new sample at 7pm)
Late evening (new sample at 9pm)
Equilibriated sample (24hrs)

So far, I do see an approx 1.0 point rise in the ph sample after equilization. I do suppose that does tell me that I am getting the right amount of CO2 in the tank. No?

Is a continued change in pH of 0.4 (from day to night) harmful to the fish?

Rob
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