test strips vs liquid reagent kit vs electronic meter

[gheitman]

I'm wondering if anyone has done a scientific experiment to test the accuracy of test strips vs. liquid reagent kits vs. electronic meters. I know the general wisdom that test strips aren't that accurate when compared to liquid reagent kits but they can't be ignored. A lot of people new to the hobby may only buy the test strips because they are less intimidating. The LFS will frequently use test strips to test water samples brought in by customers because the results are quick.

I use both the test strips (Jungle 6-N-1) and liquid reagent kit (Hagen Master Test Kit) depending on the situation. When you have 10 aquariums and want to do some quick checking the test strips provide a "quick and dirty" answer to how your water is. When you want accurate information on your pH or nitrate level (among other things) the liquid reagent kit would be better.

I'd be interested in seeing a test where three different test strips and three different liquid reagent kits are each tested by three different people and the results then compared to readings done with electronic monitors. I would do it this way because reading the results visually can be very subjective and personally I always had trouble reading the results from the API pH test kit.

 

[roka64]

That would be interesting. You would need to use the same manufacturer's brands in all three categories for best resulte, I would think.

 

[Chisel]

I am very interested in seeing these results as I use the same test strip kit (Jungle 6 N 1) and probably rely on it too much because of its convenience. So far I haven't run into any issues with the tank but if the results prove how inaccurate the strips are, I for one will be picking up some liquid/electronic kits.

 

[gheitman]

That would be interesting. You would need to use the same manufacturer's brands in all three categories for best resulte, I would think.

I don't think that you would necessarily have to use the same manufacturer's brands for the tests. It would be critical IMO however that the people doing the testing be the same for all of the tests, that the tests be done in the same tank at the same time (to avoid fluctuating levels of CO2, pH, etc.) and that the people doing the testing don't compare notes until after all of the measurements have been taken. It would be even better if there were some way to use a photometer to measure the visual test results against the color samples supplied by the manufacturer.

I would like to see one of the magazines like Tropical Fish Hobbyist do these tests. They don't even have to identify manufacturers, just show what the results of the tests are.

 

[roka64]

I agree, but different brands can have different readings. At least on the SW level. I think salifert has a more precise scale than API.

 

[Lager]

It would be an interesting experiment. We always say the strips are no good, but has anyone tested it. The test strip problem has always been once you open they get some moisture from the atmosphere,. You would need fresh strips and ones that had been open for a while.

 

[Chisel]

I agree, but different brands can have different readings. At least on the SW level. I think salifert has a more precise scale than API.

So you would recommend Salifert tests over other brands? Are aquarium Oceans "Instant Ocean" test kits any good? They seem to be a tad cheaper. Can results be that different?

 

[Kurt_Nelson]

...
I'd be interested in seeing a test where three different test strips and three different liquid reagent kits are each tested by three different people and the results then compared to readings done with electronic monitors. I would do it this way because reading the results visually can be very subjective and personally I always had trouble reading the results from the API pH test kit.

I think your paragraph above kind of hits on why results from a test like this wouldn't really tell you much. You're totally relying on someone's personal interpretation on color. Yes... it would give you an idea of how much of a "range" you might expect for a particular reading using strips vs. kits. But it would give you no idea of the true "accuracy." The strips could be 100% accurate compared to the parameter you're measuring, but because it needs interpretation - that's where the error comes in. And that's where digital meters come in... there's no interpretation - it's just a number.

However... the accuracy of a digital meter could be worse than the accuracy of a test strip. Seems like many of the digital pH meters out there are accurate to +/- 0.1 when you look at the technical specs. So that means your 8.0 pH water could really be anywhere between 7.9 and 8.1.

I used test strips quite a bit when I was cycling my tank and I came to the conclusion that they're good for detecting 0.0ppm of things. If they showed 0, then that was normally true. But if the strip showed any amount of anything, then you'd better break out the other test kits to figure out how much.

 

[roka64]

Kurt, you bring up a great point, especially determining the "true" color of the test. I have a great example. I use the API and can not read the pH test very well, where there are others that have no issues with the test.

 

[Kurt_Nelson]

Yeah... I use the API for pH also. My "normal" color is in between a couple colors... kinda. But I know what that color looks like and I do my tests in the same room, with the same lighting, every time. I don't know EXACTLY what my pH level is (I call "my" color 8.3!), but I DO know that my pH is consistent - and that's really what's important as long as it's in the proper range. To me, the actual number isn't as important as making sure that parameter stays the same.

 

[Innovator]

As Kurt stated it is not a matter of actual numbers accuracy as it is interpreted accuracy. Test strips could be used in emergency situations or even new shipment arrivals where you need to know if there is NH3 or NO2 present prior to acclimation and remedy; however, detailed results are left to the imagination. Liquid tests, imo, are better by far, but does not stipulate a proper readout in the final "drop" phase. In other words, how much of that final drop was overkill or even underkill? If you can, use a color wheel over block cards. The final outcome is guesstimation based on perception once again. Titration is better if using syringe method, but still there is a % of error (from what I've been informed, around 10%). Personally, as long as it is serviced, reagents are properly stored, and your blanks are standardized, I prefer digital and if you can afford...Spectrophotometer.

 

[roka64]

James, can I borrow your Spectrophotometer?

 

[Innovator]

James, can I borrow your Spectrophotometer?

Heh, sure, buy me one and I'll let you borrow it!

 

[cmor1701d]

Ah, one more thing to add to the "if I win the lottery" list. Oh wait. That's already on there.

I find it interesting that I can read the API pH test easily but not most others (color blind in the blue-green range).

I mostly use Salifert or LaMotte, but even they have a margin of error based on hwo carefull you are in filling the test vial, syringe and mixing between drops. I don't think a single drop difference is that great, but fillinng the syringe could be.