Problems Reading Test Kit Color Charts?

[conjuay]

When I look at the colors on the test kits that rely on matching a liquid sample to a printed chart, I'm never quite sure of what I'm seeing. The chart colors are fine, and easy to distinguish one from another. But the sample in the vial never seems to be the same as the chart colors. I always end up with a 'it could be this, or it could be that' situation.
Light reflects off the liquid differently than it does off the color swatches. For example when I do a nitrate test, the best I can say is, "Well, it's definitely not 0 ppm, and it's definitely not 20 ppm..." So I've narrowed my nitrate concentration down to about 30% of the possible range of the test.
Yet when other people present their tank's parameters, they seem to have numbers that are quite exact, as if they are testing with much more sophisticated equipment.
I guess what I'm asking is -how much of the test results reflect either the optimism or pessimism of the person conducting the test?

 

[Reef Frog]

The lighting you use when viewing the sample is important IMO. Worst is warm (yellow) incandescent light bulbs at about 3000K. The best is natural sun light at mid day on a clear blue sky day. Inside, fluorescent "daylight" bulbs ~6500K are the best. Some kits are designed to be read looking down into the test tube and others thru the side of the vial. Both should be read with the white of the card for the background and the color samples right next to it.

Another way of zeroing in on your choice is to test a known 0 sample if possible and compare to samples you make up that are high, then start diluting it to see what the colors actually look like to your eye and compare the fidelity to the sample on the card.

I guess what I'm asking is -how much of the test results reflect either the optimism or pessimism of the person conducting the test?

Good question. I think there is a good deal of perception error in test reports. The API ammonia kit is a common example. Also mistakes and variances in different lots, expiration dates etc all add up to plenty of impression with the hobby kits. I e never seen a chemical PO4 kit where I could truly tell the difference between .1 ppm and .02 ppm, making them all but useless.

 

[Maxim.dockx]

You could also be partly colorblind like me. Imagine the pain


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[conjuay]

You could also be partly colorblind like me. Imagine the pain


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Well, I can see all the hidden numbers in the color 'blind' tests and I used to have to read color codes on resisters, so I don't think that is the problem. It is more that I'm comparing a flat sample against a three dimensional object.

Reef Frog's suggestions - yeah all the lamps in the house are stained glass, I'll have to do the high noon outside test!