API test kit subjective?

[iamthelivinglight]

Ok here is what I have. A 190 gallon custom (60x30x24/LxWxH) bare bottom tank with rocks, plastic plants and homemade caves. I have two canister filters both with 9 watts UV and a 36 watt UV with flow reduced down to kill parasites. My temp is kept at 83 degrees by two jager 250 watt heaters. My water chemistry is like this consistently PH 7.0, ammonia 0 mg/l, nitrites 0 mg/l and my nitrates <5-30 ??? mg/l. So I never used an api test kit because I work in a state certified lab and have a spectrophotometer and with it my nitrates are always <5.0 mg/l. I do 33% water changes daily. I did a fishless cycle by adding ammonia 3 months ago and have been running with 8 Corry, 40 neon tetras, 1 8in. pleco, 20 fancy guppy and 5 German blue rams for 2 months. My German blue rams consist of 2 pairs and 1 extra female. The two pairs have spawned 3 time each, the eggs get ate up by the pleco. Any ways out of curiosity I bought a API master test kit and was horrified to see a nitrate reading of what looks like to me to be almost 30 mg/l. I took a sample to work and got a 4.33 mg/l reading in the Spectrophotometer. The new master kit expires in 2018. I know not every one has a Spectrophotometer at their disposal. As an experiment I have not done a water change for 3 days and each consecutive day the api has more red and less orange to it but still not all the way red, yet at work I get the same <5.0 mg/l. I know that the liquid test are far more accurate than test strips but after my experience I wonder if a lot of people are pancaking for nothing like I did. Oh and most importantly this tank was bought to be a discus tank but since I have never had the King of the aquarium before I wanted to work my way up to the crowning jewels of my tank. I have made my mind up to get them from Kenny! Now after reading this I don't really have a question it is more of a statement but I welcome some feedback and/or questions. Thank you for your time and help.

[yogi]

Thanks for sharing this information. It makes me wonder if the other tests in the kit are also inaccurate.

[myofibroblast]

Subjective in the sense that there is a lot of variability and the color gradients (between 5-20 ppm anyway) are practically up to individual interpretation. It's some iteration of the Griess reaction and the results depend on how well the reagents are mixed.

I find it amusing that some people in the aquarium hobby focus on this parameter (parameters? Parameters? Parameters?) when the results upon which they fixate are questionably reliable, if not outright poorly reproducible when obtained by commercially available kits. I think the API kit is fabulous for distinguishing whether your water has 5 or 10 ppm vs >40ppm of nitrate, but when you are obsessing over 5 vs 20ppm...lets just say dubious conclusions can be drawn from putting too much faith in those numbers. Note also that 40 vs 80 is pretty useless on that API color card, though really a WC is usually in order when you are in that stratosphere of nitrate level regardless of the true value.

I don't doubt that some people will have the dexterity and good fortune to have reagents that never change in concentration due to evaporation or uneven mixing, and that their test water volume are always the same, and their drops are equal volume each time. But I suspect this isn't the case more often than not.

What is worse than not knowing how to interpret a test result is interpreting the results incorrectly (or not knowing the limits of your tests).

BTW, is that spectrophotometer reading UV wavelengths (i.e. Reagent-free)? Just curious.







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[iamthelivinglight]

Those are good examples of the objective nature of the test, not to mention a myriad of other factors that lead to deferring results by different people analyzing even the same sample by eye. We use Hach’s DR 6000 UV-VIS Spectrophotometer and we use the TNTplus vials, no reagent blank necessary, the reagent is in the cap. Thank you for the eloquent repartee! I figure that if my German blue rams are thriving and spawning it will be safe to add my discus. The api master test dose a good job with pH, ammonia (@0.0 mg/l), and nitrites (@0.0 mg/l).

[iamthelivinglight]

I replied to this yesterday morning however it was flagged for a moderator to review it. I had no pics, URL, or anything else so I am not sure why it got flagged. Anyway thank you for the stimulating repartee. The spectrophotometer is UV/VIS no need for reagent blank but there is a reagent in the cap of the proprietary vile, then I add my 1 mil sample to the vile. The api test kit has given easy to read results for pH, ammonia, and nitrites. Thank you for your time and help.

[Second Hand Pat]

It was flagged due to @ being part of the post. I suspect the forum software is considering the @ as part of an email address.

[iamthelivinglight]

Thank you Pat I understand now. Thanks again for your time and help.