So before keeping fish from a local drainage for a big tank build I have coming up, I want to get a feel for the water paramters at a couple of different potential collection sites, and at different times of year. The basics i want to test for are the same thats in the basic API kit (frankly I'm just plain curious about nitrates anyway, since its surrounded by fields for much of its length), as well as GH, KH, and TDS. I would also like to try and figure out how to test for dissolved O2, but thats going to take some research and probably equipment still, so might get dropped to the bottom of the list.
Anyhoo, my question is about the turbidity of the water to be tested. Since this is a farmland river in the middle of Illinois, there are very few times when its actually clear. With that in mind, how should I approach tests that are based on comparing the color of the solution? Surely turbid water will skew the color of the sample? Are there ways to treat the water that will still give accurate results?