How test PH with API tubes in CO2 injection - The Planted Tank Forum
 
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post #1 of 8 (permalink) Old 09-01-2012, 09:49 PM Thread Starter
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How test PH with API tubes in CO2 injection

Hi there,


I was wondering about testing ph with an API test kit. Dunking the test tube in the water, do I then wind up disperse co2 from the sample, throwing off the main purpose of my test?

My main purpose is to monitor changes in ph when my hard water is exposed to my co2 system.
I have co2 from a canister with solenoid, etc. and an external reactor in my 55g.
I have co2 on morning to evening and then off for the night.
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post #2 of 8 (permalink) Old 09-02-2012, 12:30 AM
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If I understand the question, yes, you will be getting a reading with the CO2 mixed in the water. But then that is not really a problem. The tank PH will vary during the day and night but it is normal. The plants and fish work to change the PH all the time. What we read about PH being super important is often not what many people find as true. Holding somewhat steady without sudden swings is good but the small variation over the day is not important.
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post #3 of 8 (permalink) Old 09-02-2012, 02:50 AM
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Remember, almost everyone who uses high or even medium light also turns off the CO2 at night. This allows the CO2 in the water to outgas, leaving the pH around 1.0 higher than it was when the lights went off. When the lights come back on, or an hour or so before, the CO2 is turned back on, and within a half hour or so the pH is back down by 1.0 or so. That clearly shows that big pH changes are irrelevant.

When you don't use CO2, a big pH change can be a symptom of problems with the tank water. But, ordinary good tank/water maintenance eliminates that problem, so monitoring pH except as a way of verifying that you are getting CO2 dissolved into the tank water is of little value. My present tank setup, now about 6 months old, has never had the pH measured.

Your specific question was about dipping the test kit test tube in the tank to get a sample to test, and whether or not that changes its CO2 content. I haven't tested that, but intuitively I know it does, but probably not fast enough to make your pH measurement incorrect by enough to worry about. A possibly bigger concern would be that the CO2 concentration, and pH, is not the same all over the tank, and, for most tanks with good surface ripple, the surface water would be at the lowest CO2 concentration, so the pH of that water wouldn't be at all typical of the whole tank. If Plantbrain reads this, I'm sure he has tested this and can tell us how big this effect is, if it even exists.

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post #4 of 8 (permalink) Old 09-02-2012, 03:01 AM Thread Starter
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Thanks!
I would like to check my ph from time to time, or at least one time.

My question is, if CO2 injection lowers the ph, then wouldn't my test tube and my hand disperse the CO2 as I collect water? That is, just as vigorous surface action from a powerhead loses CO2, is the water that gets in the test tube not similarly stirred up? And therefore wouldn't the ph reading be different from what it would have been had I not stirred it up?

I am just wondering about the technique of testing ph, with co2 injection. I take it from one answer that yes, it would be a different ph than in the tank left as it is.
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post #5 of 8 (permalink) Old 09-02-2012, 05:01 AM
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CO2 isn't affected by stirring up the water, except at the water to air surface. The effect is loss of CO2 to the atmosphere, so that doesn't happen down in the water. If I was concerned I would stick the tube in the water open end down, then rotate it to let water in and air out. Then pull it back out and drain it down to the 5 ml line. Then quickly do the pH test before the CO2 in the water escapes to the air.

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post #6 of 8 (permalink) Old 09-02-2012, 01:00 PM
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Are you looking at this thread? http://www.barrreport.com/showthread...nown-reference
He is using a ph meter to do this, I will be asking what is the best model to use and trying it for myself.
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post #7 of 8 (permalink) Old 09-02-2012, 01:30 PM
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I use a ph test tube. I pull water with a 5ml medicine dropper. Testing multiple points in the tank does not give varying results that are visible to the eye. If the ph looks to be 6.4 from surface water, it also looks that way at the bottom rear corners.. good flow may help this but i dont think u will get a noticeable difference. The co2 itself doesnt so much make the water acidic. Its the resulting carbonic acid formed because of co2 being in the water. It will be diffused throug the tank much better than a dissolved gas would so ph testing in different locations is not a good measurement of co2.

This is my experience though. The only accurate tester i have is an oxygaurd portable co2 reader. The rest is titration kits and one tds meter

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post #8 of 8 (permalink) Old 09-02-2012, 03:09 PM Thread Starter
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Thanks!

I don't see how getting deep water in the tube helps, since when you pour off excess it's the same as shaking around the entire surface of your tank, on a miniature level.

I do look forward to hearing about the meter, can u post back here?
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