With new water, I like to start with Di-chlor rather than bleach because it adds some CYA. Bleach is FINE and ALWAYS the best way to chlorinate, but you DO need CYA, as Dave S. says. Tri-Chlor pucks in a floater is also very good at this point because they add CYA and give a constant flow of chlorine. It's just very hard to buy small amounts of Di-chlor or pucks--then you are tempted to use them up, overstabilizing your water, when you should have switched to bleach.