pH Probe - Issues? Advice? Answers? - The Planted Tank Forum
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post #1 of 3 (permalink) Old 01-23-2013, 09:46 PM Thread Starter
Algae Grower
Join Date: May 2009
Location: Savannah, GA
Posts: 17
pH Probe - Issues? Advice? Answers?

Ok, so I am getting my tank back together after a slight hiatus. I had some 7.0 calibration solution in a bottle that hadn't expired so I tested my probe's functionality. 7.1. Great! Didn't have any 4.0 so I ordered some. It arrived today but I am getting ahead of myself.

I tested, just to be sure, the calibration solution with my handy dandy API pH test kit. It read wellllllll below 6.0. That's not good me thinks. Did some reading. Turns out all my test kits were expired. Good thing. I had some old pH test reagent. Ordered some more up. Tested it again when the new stuff arrived, same result. Figured my pH solution was bad since it was opened, albeit capped, but still ruined somehow, perhaps I contaminated it? Who knows.

Well, the new calibration solution arrived today. Tested my probe (which I had left 'calibrated' to the 7.0 from the 'contaminated' calibration solution) and it read 7.0. I was surprised but it read 7.0! Checked the 4.0, it read 3.9 - adjusted the slope.

So, I know that AQUARIUM pH test kits probably only work on aquarium water but does anyone know why? Did some reading on Google but no real clear answer.

Thanks in advance!
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post #2 of 3 (permalink) Old 01-23-2013, 10:15 PM
The Security Dude
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Location: The Badlands
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How did you store your probe? or is it a PH pen? API test kits are pretty good how old is it. Sure you are using the fresh water and not the salt chart

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post #3 of 3 (permalink) Old 01-23-2013, 11:25 PM Thread Starter
Algae Grower
Join Date: May 2009
Location: Savannah, GA
Posts: 17
Sorry, should have said what I had! It's a Milwaukee SMS122 pH controller. It has been stored in the fish tank wet and is about three months old. The pH kit I just bought and the expiration date is in 2015.

I ran into something similar where the ammonia test kit I was using kept reading positive for 4ppm or so (really green!) even out of the tap. Turns out our county changed to using chloramine instead of chlorine to sanitize the water. On the particular kit I was testing with it would give a positive reading if chloramine was used to sanitize the water. I don't specifically recall why but the explanation I read made sense and when I bought a kit that wouldn't test false positive, magically there was no ammonia.

I think it may have to do with ionization of the water or something because when I was doing all this, DI water was testing below 6.0 with the API pH test kit and in reading on that, since I was always under the assumption that DI would should be about 7.0, turns out from what I gather that DI doesn't have much in the way of ions and can be subject to pH swings? When I tested the DI water using the pH meter (the SMS122), it read 6.9 (I think at least - much closer to where it needed to be). This leads to to think the type of pH test that the API test kit is designed for won't read these types of solutions accurately.

At least that what I am thinking, so that's why I asked here!
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