I'm not sure about the water temp. I know that in a local public lake the shallow areas where the sunlight could get to the muck bottom had 4°F-5°F higher water temp than the rest of the lake in the Spring.
As for the black dye, plan on using about 30% more to limit visibility as compared to the blue dye. For some reason the black dye that we have used didn't seem to be as "dense" as the blue. Both dyes from the same mfg.
