Which test kit is correct?

[AJE]

I was comparing my api test kit to my aquarium coop test kit and they show opposite ph. My api one shows that I have a ph around the higher end and my coop one shows it’s around the acidic end. Which is more accurate?

[CosmicAshhole]

This is why I don't trust strips. 

I keep trying, but they keep giving me weird readings.  Maybe I'm crazy.

[AJE]

On 6/12/2021 at 1:48 PM, CosmicAshhole said:

This is why I don't trust strips. 

I keep trying, but they keep giving me weird readings.  Maybe I'm crazy.

Yeah both the api and these strips give me these readings so one of them is consistently wrong. I don’t know which. Maybe I’ll take some of my water to an lfs and which ever they test closer to is the one that is trustworthy 

[Koi]

This isn't the most surefire way but if you have distilled water you can test that and see what results you get. The results should come pretty close to 7 but most likely it will be a little lower due to co2 dropping the ph of the distilled water.

[Patrick_G]

I’ve tested one of my Coop strips against a known PH solution and it was accurate. I think it’s key to make sure your reading is made exactly one min after you swirl it in the water. 
You can buy calibration solution on Amazon if you want double check accuracy yourself. 

Edited June 13, 2021 by Patrick_G

[CT_]

In my experience with the api kit, two brands of test strips (including the co-op strips), and a lab ph meter, and a cheap ph meter, there are certain water conditions that make the test strips read considerably lower. 

I'd believe the API kit since it always agrees with the lab ph meter.

I have a hypothesis about why that is now but I haven't been able to test it yet.   😞

 

On 6/12/2021 at 11:30 AM, Patrick_G said:

I’ve tested one of my Coop strips against a known PH solution and it was accurate. I think it’s key to make your reading is made exactly one min after you swirl it in the water. 
You can buy calibration solution on Amazon if you want double check accuracy yourself. 

I think the problem with testing against buffered solutions is that all tests have been validated to work with those solutions because that's the easiest way to test them.  I think to understand where the strips, meters, and solutions differ you have to look at whats different from test solution water and tank water. 

EDIT: to put this another way.  i bet you'll find all methods work great with buffers even if they disagree with tank water.

Edited June 12, 2021 by CT_

[AJE]

On 6/12/2021 at 2:30 PM, Patrick_G said:

I’ve tested one of my Coop strips against a known PH solution and it was accurate. I think it’s key to make your reading is made exactly one min after you swirl it in the water. 
You can buy calibration solution on Amazon if you want double check accuracy yourself. 

Yeah I took the picture right at the 1 minute mark 

[Fish Folk]

@Koi and @Patrick_G -- thanks for these helpful tips! Very practical for questions like this.

I'm wondering aloud if there's possibly any testing readings are skewed due to the use of various water treatments? Lately, I've been using FritzComplete for water treatment . . . and I wonder if the cocktail mixed up there could mess up test results?

Edited June 12, 2021 by Fish Folk

[Patrick_G]

On 6/12/2021 at 11:49 AM, Fish Folk said:

@Koi and @Patrick_G -- thanks for these helpful tips! Very practical for questions like this.

I'm wondering aloud if there's possibly any testing readings due to the use of various water treatments? Lately, I've been using FritzComplete for water treatment . . . and I wonder if the cocktail mixed up there could mess up test results?

It makes sense based on what @CT_ pointed out above. 

[Koi]

@AJE It looks like theres some extra water dripping from your test strip onto the color chart.

This probably isn't the issue you are running into but I'll just throw this idea out there anyways

Sometimes when I lay test strips flat on a table the water tends to seep through the back and turn the nitrite pad pink (sometimes my ph and kh pads too). Now after I dip my test strips, I just lay it on top of my tongs so that any excess water can drip off without touching the other pads.

[Koi]

On 6/12/2021 at 11:49 AM, Fish Folk said:

@Koi and @Patrick_G -- thanks for these helpful tips! Very practical for questions like this.

My pleasure!

I'm pretty sure my method isn't the most accurate for calibrating a test kit but I can sleep better knowing at least one of my results is close!

[sairving]

I started with the tetra test strips and then bought an API test kit.  The results were always the same for the ph test.  GH and KH were another story.  Our well water is so hard that the resulting color would not even be shown on the results chart.  API just has you count drops until the color changes.  Every few years we test the water with well water test strips.

[B1gJ4k3]

I'm glad I'm not the only one who is seeing inaccurate results from pH on the Coop test strips. I can't get anything above 6.4-6.8 on any of my tanks, even the ones where I'm using crushed coral to buffer up to 7.6.

[ARMYVET]

I can tell you that I have a digital PH pen that Is calibrated regularly.  The Co-Op multitest strip matches up very very close to my pen.

I can say that for me it also matched up with my API kit.  May I ask what dechlorinator you are using....some dont react well with certain test kits whether it is liquid or test strip. 

I can also say that my TDS meter lines up with the GH pad on the multitest strip as well.  My tds Meter shows 0 coming out of my R/O filter so I know it is reading correctly.

This is just what I have experienced.  

Edited June 16, 2021 by ARMYVET

[AJE]

On 6/16/2021 at 1:35 PM, ARMYVET said:

I can tell you that I have a digital PH pen that Is calibrated regularly.  The Co-Op multitest strip matches up very very close to my pen.

I can say that for me it also matched up with my API kit.  May I ask what dechlorinator you are using....some dont react well with certain test kits whether it is liquid or test strip. 

I can also say that my TDS meter lines up with the GH pad on the multitest strip as well.  My tds Meter shows 0 coming out of my R/O filter so I know it is reading correctly.

This is just what I have experienced.  

I am using the fritz dechlorinator.

[AJE]

I just got back from the pet store, they tested the water for me and they say my water is around 7.8. So 2 against aquarium co-op test kit. This is pretty disappointing, I really wanted the test kit to work but it looks like it doesn't. Could there be an another reason to this @Cory?

[Cory]

On 6/20/2021 at 11:52 AM, AJE said:

I just got back from the pet store, they tested the water for me and they say my water is around 7.8. So 2 against aquarium co-op test kit. This is pretty disappointing, I really wanted the test kit to work but it looks like it doesn't. Could there be an another reason to this @Cory?

I'm not sure what's causing your results. Are you on tap water? well water etc? I did a video of testing pH with a calibrated solution. Added in nitrates and hardness to the test as well.

 

[AJE]

On 6/20/2021 at 4:58 PM, Cory said:

I'm not sure what's causing your results. Are you on tap water? well water etc? I did a video of testing pH with a calibrated solution. Added in nitrates and hardness to the test as well.

 

I am on city water but all three of the tests were done on water from my fish tank. I do have crushed coral in the tank, could that be the issue?

[Cory]

On 6/20/2021 at 2:05 PM, AJE said:

I am on city water but all three of the tests were done on water from my fish tank. I do have crushed coral in the tank, could that be the issue?

I don't think crushed coral would do anything to our test specifically. Can you do a test with your tap water with our strip and another test to eliminate possibly any factor from the aquarium? If that test works, then we know, ok something is reacting with a chemical in that tank. It's really strange to me so far. I'd like to get it figured out.

[AJE]

On 6/20/2021 at 5:07 PM, Cory said:

I don't think crushed coral would do anything to our test specifically. Can you do a test with your tap water with our strip and another test to eliminate possibly any factor from the aquarium? If that test works, then we know, ok something is reacting with a chemical in that tank. It's really strange to me so far. I'd like to get it figured out.

I got the same results out of the tap

[Cory]

What state/count do you live in? I'll try looking up their water report.

[AJE]

On 6/20/2021 at 5:29 PM, Cory said:

What state/count do you live in? I'll try looking up their water report.

I live in Fayette County, Kentucky

[AJE]

Here is a picture of a test I took April. The ph is still wrong but the chlorine showed up but the test I just took shows that I don’t have any chlorine. Maybe they have lowered how much chlorine they are putting in since then and it is low enough to where it doesn’t register. I don’t know, weird

[CT_]

@Cory  I got some time to test my hypothesis and I think I figured it out.  I've spent a LOT of time in the last month thinking about this and trying to figure it out.

Acidic soft water can be bad for pipes so some water districts add sodium hydroxide, a strong base to up the PH. 

If its the ph indicator I think it is in the strip then its also an acid.  Since almost all of the NaOH dissociates when dissolved into water it doesn't have much buffering capacity.  This means a relatively weak acid like the ph indicator can bring ph down.  Liquid tests, use much more water (100x) and probably less indicator (and also different indicator) so they don't change the pH as much. 

To test this I mixed distilled water with two tiny granules of sodium hydroxide and measured the ph with both my meter(>11) and the strips (<7).  Since 11 is out of range I thought maybe the test results could be invalid (though my understanding of the chemistry is that it should max out the red color if the sample ph remained at 11 on the strip).  So I diluted it down until the ph was stable around 8 (I hit something like 7.8 which is close enough), and tried again, same result strips show <7.

Here's some photos of my experiment:

just distilled water freshly opened.  says 6.7 but there's nothing in it right now.  Just to illustrate sane results with just water on my probe.

two granules of lye + lots of stirring and waiting for measurement to settle down:

I moved 1-2 teaspoons of the ph 11 water into fresh distilled water until i got a stable reading close to 8.

[AJE]

On 6/20/2021 at 6:01 PM, CT_ said:

@Cory  I got some time to test my hypothesis and I think I figured it out.  I've spent a LOT of time in the last moth thinking about this and trying to figure it out.

 

Acidic soft water can be bad for pipes so some water districts add sodium hydroxide, a strong base to up the PH. 

 

If its the ph indicator I think it is in the strip then its also an acid.  Since almost all of the NaOH dissociates when dissolved into water it doesn't have much buffering capacity.  This means a relatively weak acid like the ph indicator can bring ph down.  Liquid tests, use much more water (100x) and probably less indicator (and also different indicator) so they don't change the pH as much. 

 

To test this I mixed distilled water with two tiny granules of sodium hydroxide and measured the ph with both my meter(>11) and the strips (<7).  Since 11 is out of range I thought maybe the test results could be invalid (though my understanding of the chemistry is that it should max out the red color if the sample ph remained at 11 on the strip).  So I diluted it down until the ph was stable around 8 (I hit something like 7.8 which is close enough), and tried again, same result strips show <7.

 

Here's some photos of my experiment:

just distilled water freshly opened.  says 6.7 but there's nothing in it right now.  Just to illustrate sane results with just water on my probe.

two granules of lye + lots of stirring and waiting for measurement to settle down:

I moved 1-2 teaspoons of the ph 11 water into fresh distilled water until i got a stable reading close to 8.

Interesting. So does this mean just the ph is inaccurate? Can I trust the other parameters?