A little off topic, but bstreep, you said you were a molecular biologist and I was just curious if you were still working as one and where you went to school at? I am also a molecular biologist so its always good to meet others with the same interests.

And just to throw in my 2 cents about test kits. IMO the only way to go to get truly accurate results is to use a a spectrophotometer instrument like the ones made by Hanna that read the "color" for you and use powdered reagents as well. These are very expensive but will give you the most accurate results short of using an even more expensive nutrient analyzer.