QA, I am hoping some others chime in but your late afternoon surface readings seem (IMHO) to be indicating lower than they probably actually are. These readings of surface water should be near saturation IHMO (saturation would be about 8.4). Are you confident in the instrument's calibration?.........
Thinning the crawdads appears to be making a big difference on your water clarity.
I have cross checked the DO Meter with my Chemtech vial test kit, on occasion, and my confidence level is high.
I will remove more craws next year, if necessary, to further improve clarity but for now I am happy with some improvement. The water tends to clear up in the winter months anyhow.
EDIT: for clarification, when I say surface DO I am talking about the top 6" as the meter that I use has a 5" head on it that must be moving in the water to get a good reading. I bob it up and down as close to the surface as I can which means it's reading somewhere in the upper 6 inches.
Oddly enough I have measured DO levels as high as 11ppm at the surface, but just 24" down it was 4.8ppm.
