'Normal' fresh water from wells or utilities can be anywhere from ~6.5 to ~8.5. You are correct; you don't need borax at present.

Pristine Blue residue would just be copper -- leaving your filter blue, green, or maybe grey. You can remove any such residue with an acid wash, but make 100% sure you clean it with detergent FIRST. Here's a cartridge HOW-TO: http://www.poolforum.com/pf2/showthread.php?18044