Then again, do we have reason to suspect that there's a lot of cutting the SN going on ? It's a cheap industrial supply, not an illegal street drug.
The blood test, where some blood gets mixed with some SN also doesn't scream high precision. But if the aquarium test turns sorta pink and the blood sorta dark, it might well be enough. Where I am, the 50lb bag goes for $35. What would they cut it with that's cheaper ?