Cheap bleach for those in the midwest.

[BigDave]

I believe the difference in the label of 15% available chlorine and 12.5% sodium hypochlorite may be difference in units - weight vs concentration.
The difference in test results has to do with freshness. Bleach (sodium hypochlorite solution) degrades very quickly when exposed to warm temperatures and sunlight. The manufacturer / packager bottles it at a higher concentration than the label in the hopes of still having the label concentration when it gets to the store.

[OOsever]

The stuff I bought was still in the 4 pack cardboard carrier. There were several loose bottles floating around the display but since chlorine can degrade under sunlight I opted for those in the boxes. Mine had manufacturers date stamps of June 2012, so they were relatively fresh.

[waldreps]

The stuff I bought was still in the 4 pack cardboard carrier. There were several loose bottles floating around the display but since chlorine can degrade under sunlight I opted for those in the boxes. Mine had manufacturers date stamps of June 2012, so they were relatively fresh.

Yeah, I guess yours was fresher than mine. There were no cardboard boxes at my store. They were all loose and on display. I got the ones in the back hoping that they would be better.

[Pipecrew]

How would a gallon of 6% bleach compare to a 1lb bag of shock?

[OOsever]

Would depend on the contents of the "shock". If it was dichlor then as far as chlorine goes its pretty close to the same dose as a gallon of 6% bleach. (Though bleach normally comes in 96oz containers) If it was cal-hypo then it would depend on the percent concentration on the packaging. However both dichlor and cal-hypo have effects on other areas of pool chemistry. Dichlor will raise your cya and cal-hypo your calcium hardness. If you need a boost in these areas then it's probably not such a bad thing to use them occasionally but not as your primary source of chlorine, even if you do find some super cheap.