Need 2nd Opinion on % vs Volume vs $ calculation/assumptuion

[giroup01]

The point of that is that you'll read on the jug "Guarantee: Sodiun Hypochlorite: 10.8%" then when you test a fresh batch you'll come up with "Available chlorine content" of 10.3% and think the batch is not fresh.

The original poster is looking at 12% sodium hypo from the pool store and measures the chlorine content at 10.3% then comments "I guess that's not too bad. I never realised the conc could drop so much."

The 12% is sodium hypo concentration, the 10.3% is chlorine content, technically he's comparing two different things. (He also mentions "Bleach concentration = 11.5-1.2 = 10.3ppm = 10.3%", that's not bleach concentration, that's active chlorine concentration).

And also, keep in mind the "parts per million" is a weight to weight measure, you must consider the solution density in your formula. 12% bleach is heavier than 3% bleach.

All these details add up.