blue calcium carbonate in fresh sw?

so i always have this issue when i mix salt where i get about a pinch of calcium carbonate precipitate granules after mixing about 15 gallons worth in a rubbermaid, no matter what i try (cold temp mixing, tank temp mixing, heating during mixing and heating only after, aerating during mixing and not, using my hand aswell as a maxijet 1200 to keep everything suspended, sprinking salt in all the way up to dumping quarter cups in at a time) i always get this residue.. okay, i can deal with that. what im concerned with is that this time i mixed my new box of fritz RPM salt in 15 gallon of RODI and after the mixing was done i saw a small pinch of same sand granules only with a copper sulfate looking blue tint to them.

does anyone have experience dealing with and using fritz RPM in their setup and came across this issue ever?