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Test Strip Troubles


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Alright so I recently picked up some test strips from the Coop. I tested on of my seasoned tanks and got a reading of 6.4 ph. (Tank has crushed coral mixed in with gravel). After testing with the strips I tested with my api liquid test kit because the 6.4 reading seemed way off what I usually keep my tanks at. The api kit gave a reading of 7.2 ph. I repeated these tests several times on multiple tanks all with the same result of my ph reading low on all my tanks according to the test strip and around 7.2 with api kit. My question is could there be somthing in my water affecting the ph reading on the strips? All other measurements on the strips match up (within reason) with the api kit. I love the strips im just lost on why I keep getting a reading of 6.4. If anyone has any inside ide appreciate it.

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FYI @OrdinaryGamertag @Rosanne @SWilson, Cory just posted a video on how he tested the pH and nitrate strips with known solutions.

That being said, I have had similar issues with the results from the API pH test not matching the results from pH test strips (from multiple companies). After researching into my city's water treatment methods, I found out they are artificially raising our tap water's pH using a lime slurry process (because the higher pH kills off certain pathogens). I'm not a chemist, but my theory is that whatever reagents are commonly used in pH test strips are not able to detect or react to whatever is artificially raising my water's pH. 

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42 minutes ago, Irene said:

FYI @OrdinaryGamertag @Rosanne @SWilson, Cory just posted a video on how he tested the pH and nitrate strips with known solutions.

That being said, I have had similar issues with the results from the API pH test not matching the results from pH test strips (from multiple companies). After researching into my city's water treatment methods, I found out they are artificially raising our tap water's pH using a lime slurry process (because the higher pH kills off certain pathogens). I'm not a chemist, but my theory is that whatever reagents are commonly used in pH test strips are not able to detect or react to whatever is artificially raising my water's pH. 

Ya I figured it was somthing like that going on. I know Cory and the team test stuff alot so I had no doubt that the strips should have been accurate which made me belive their was some outlying factors

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1 hour ago, Irene said:

I'm not a chemist, but my theory is that whatever reagents are commonly used in pH test strips are not able to detect or react to whatever is artificially raising my water's pH

I'm not a chemist either, but I don't see how this is possible.  All a pH indicator is doing is detecting concentration of hydronium ions.  Shouldn't the lime slurry used to "artificially" raise pH have the same effect as water having high pH because it flows through limestone?  The "artificial" lime slurry is just calcium carbonate (which is the main component of limestone) of magnesium carbonate (dolomite) heated and converted to calcium oxide or calcium hydroxide.  Either way, addition of lime will make fewer hydronium ions available, thus raising the pH.  

What could possibly be going on is these two products use different pH indicators.  I think API regular pH indicator uses bromthymol blue, and I have no idea what Aquarium Co-op's uses.  pH indicators can be affected by the buffering capacity of the water.  If you have water with very low KH, I guess that might affect certain pH indicators - and liquid indicators are more likely to be affected because they are using larger quantities of water.

Huge, enormous caveat here: I am not a chemist!!!!  I am speculating here, hoping that someone who IS a chemist will jump in and tell me I'm wrong, right, or partially right, and provide a correct/better/more accurate explanation.

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Posted (edited)

@Jess Interesting! I didn't know that low KH could make pH results unstable, but this article seems to say the same thing. API test kits usually say I have pH 7.8-8.2, 3° GH, and 3° KH, whereas the test strips usually bottom out and say I have pH 6.2-6.4, which is a pretty wide discrepancy. Maybe the pH test strips never changed color because of the KH, but I didn't think 3° was that low.

 

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7 minutes ago, Irene said:

API test kits usually say I have pH 7.8-8.2, 3° GH, and 3° KH, whereas the test strips usually bottom out and say I have pH 6.2-6.4

That's really weird.  I would have thought liquid test kits would be more likely to be inaccurate.  That said, I would guess that API - with all their knowledge and reputation - definitely understands all of this much better than me and would adjust/create their kits to avoid this problem, knowing that they'd be used in a variety of water conditions.  

I'm out of ideas there!  Your situation is very strange to me.  My water is about the same as yours, and I think it is also treated in a similar way.  But I have aquasoil and pressurized CO2 in my tanks, so that lowers my pH to around 6.2-6.4.  I don't have the Co-op's test strips yet, but my Tetra strips and API kit both are very consistent on pH.  

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59 minutes ago, Jess said:

I'm not a chemist either, but I don't see how this is possible.  All a pH indicator is doing is detecting concentration of hydronium ions.  Shouldn't the lime slurry used to "artificially" raise pH have the same effect as water having high pH because it flows through limestone?  The "artificial" lime slurry is just calcium carbonate (which is the main component of limestone) of magnesium carbonate (dolomite) heated and converted to calcium oxide or calcium hydroxide.  Either way, addition of lime will make fewer hydronium ions available, thus raising the pH.  

What could possibly be going on is these two products use different pH indicators.  I think API regular pH indicator uses bromthymol blue, and I have no idea what Aquarium Co-op's uses.  pH indicators can be affected by the buffering capacity of the water.  If you have water with very low KH, I guess that might affect certain pH indicators - and liquid indicators are more likely to be affected because they are using larger quantities of water.

Huge, enormous caveat here: I am not a chemist!!!!  I am speculating here, hoping that someone who IS a chemist will jump in and tell me I'm wrong, right, or partially right, and provide a correct/better/more accurate explanation.

One thing to remember about any indicator (which is the chemical that changes color depending on pH) is that they tend to be very chemically reactive.  There are tons of them out there, and some you can even make at home (For example, red cabbage can be used to make an indicator that is blue at ~7 pH, green at basic pHs, and red at acidic pHs).  It could very well be that the chemicals API uses in their liquid pH tests and the chemicals in the co-op indicators are different, and may have differing reactions to other chemical species floating around in the water being tested, besides just looking at H+/OH- concentrations.  Most indicators used for aquariums tend to have fairly narrow ranges where they change colors, and I can imagine it not taking much else in the water to throw them out of whack.  It could be as simple as the indicator used by one gets thrown off by iron content in water, vs  the other one is completely unaffected by iron in the water (or any other thing that could be dissolved in your tank water).

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I am relatively new to the hobby and I think I have read every thread about the Coop test strips and other testing kits trying to figure out which one to use.

I, too, have struggled with the Coop test strips... and every other test I’ve used... due to reading colors - not necessarily because one is more accurate than another.

I took a water sample to my LFS recently and had them run their tests along side all 3 of my options...

With extra eyes, many that are better at colors than mine, I was able to discern that the result of each test (Fluval liquid, API liquid, Coop test strips, & whatever the store used) were all reasonably close for my purposes.

In the end, my conclusion was that finding something that works for my eyes and then just “watching the trends” is more important than finding an absolute value on any of them.  Ultimately, I will use the API test as my “standard” as that is the easiest color chart for my eyes.

Using the Coop strips, my pH could be anywhere from 6.8 to 8.0 because I can’t tell the difference in any of those colors. However, I like the Coop strips for quick checks of nitrite/nitrate... to me, ANY discernible color on those means it’s time for a water change.  Does this mean the tests aren’t accurate?  NO!  Just that I can’t “see” the results. 

All that said, since changing to tap water instead of buying/hauling RO water, I did find out that my new community of tetras is running close to 8.0 pH.  My LFS runs RO water in the store, so I need to work out a way to bridge that gap so I don’t lose more fish due to shocking them. (Yes, all other parameters are good, so assuming it’s the pH jump) My African cichlid tank is actually a little on the high side, too, as it’s in the high 8s to low 9s.

Like many things, I think it’s mostly about finding a balance in something that works for us as individuals and our aquariums.

 

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14 minutes ago, LaurieinIA said:

I, too, have struggled with the Coop test strips... and every other test I’ve used... due to reading colors

This raises another important point.  Variance in individuals' color perception (due to an extreme, such as color blindness, or something more subtle) will affect colorimetric tests.  Variance in the ambient lighting will, too.  

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Posted (edited)

Color differential is an imperfect method for accurate reading of anything.

MANY people interpret color differently from any base standard, not many have anything near “calibrated” color sight.

Often overlooked, also, is the fact that what a human interprets as certain color (or shade) is not really that objects “color” at all, but the color (wavelength) of the light reflected off its surface.  This means that the light present (and amount of) is also a variable factor.

An objects “color” (particularly subtleties of shade) can appear much differently when presented in different types of light.

For example...

A color standard viewed in bright sunlight, will appear very different when viewed indoors, under artificial lighting.  What a color looks like indoors, under incandescent lighting, Is different when viewed with fluorescent lighting, and so forth.

This scenario is compounded when trying to ascertain subtle differences in shading, which is exactly the problem with both the color strips and liquid tests kits.

There’s an easy solution to this.  Buy yourself a digital pH meter and this problem goes away.  Numbers have no “shade” to interpret. A “2” is always a “2”, a “7” always the number that follows 6, et. al. 
 

These units are pretty inexpensive now, just make sure you source one that is temperature compensated (most are) and calibratable (some are, some are not).  Keep it calibrated (it’s easy to do) and the color interpretation problem goes away forever (for pH anyway).

P.S. - There is a “caveat” to the postulation I have put forth.  Waiting to see who’s the first to notice...

Edited by tonyjuliano
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4 hours ago, Irene said:

FYI @OrdinaryGamertag @Rosanne @SWilson, Cory just posted a video on how he tested the pH and nitrate strips with known solutions.

That being said, I have had similar issues with the results from the API pH test not matching the results from pH test strips (from multiple companies). After researching into my city's water treatment methods, I found out they are artificially raising our tap water's pH using a lime slurry process (because the higher pH kills off certain pathogens). I'm not a chemist, but my theory is that whatever reagents are commonly used in pH test strips are not able to detect or react to whatever is artificially raising my water's pH. 

I've seen Cory talk about all the testing on the live stream a few times and I have no doubt they're accurate under the conditions tested.  But I feel like he's gas lighting (probably unintentionally) a bit about their accuracy and ease of use by saying how easy they are for his employees to use and how accurate* they are in his tests.  The conditions of my aquarium cause my pH to be read way lower than it actually is on ALL test strips and GH to read off too (though the ACO ones are consistently closer).  I posted about this a month or so ago and Cory said he wanted to get to the bottom of it but never followed up.  I did my own investigating since I have the resources to do so, and found ways to get better results on some tests but never figured out why ph strips work so poorly in my water.

 

*: I'm talking about significant differences ph 7 vs 8 or gh 140 vs 300. 

 

 

 

@Irene I've also found out my water supply has added sodium hydroxide to raise the pH and prevent pipe corrosion.  Lime slurry is calcium hydroxide.  I wouldn't call either of these additives artificial in the sense that the pH increase is fake, but they are artificial in the sense that the water doesn't naturally have those.  I wonder if metal hydroxides interfere with the ph pad's chemistry somehow. 

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