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Does anyone know why an API Nitrate test would show a brown color on the addition of the first reagent? I'm in the middle of a cycle and at a point where the Ammonia test showed 0 ppm and the Nitrite showed 1-2 ppm, but I suspected a small drop in nitrites, I decided to check Nitrates. When I added the 10 drops from the first reagent to the tank water the color turned to a brown instead of the expected yellow. When I tested tap water I got the proper yellow so I don't think it's the reagent.

The contents of the tank are egg crate, a small amount of silicone, Pool Filter Sand, sandstone from a local landscape supply, Matrix in plastic media bags, Jebao return and wavemaker pumps,Finnex titanium HMX Heaters and nylon mesh and polypropylene felt filter socks.

Any ideas are welcome.

Thanks

GCG
 

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Not sure if this is the explanation but you cannot get an accurate nitrate reading on the API test when nitrites are present. No point checking them till nitrites are at 0.
 

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This is a guess since I don't know parameters of your water, but sometimes that sort of thing will happen if some other chemical is at an "outside the norm" range. I know in swimming pool testing, if you're shocking your pool with high levels of chlorine, the standard pH tests are uselessly unreliable and the hardness tests (which are titration based) go to completely different start and endpoint colors.
So I'd say that you need to wait until nitrites are 0 and try again. It could be that the nitrites were the culprit. (Nitrate tests often work by converting the nitrate to nitrite and then measuring the level of nitrite, that's why they're not useful with non-zero nitrite levels.)
 
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