Yes, you are right. Diluting the concentrated solution in half will significantly extend its life. It is also correct that as the chlorine breaks down its rate of breakdown will slow down, but note that the half-life takes that into account -- the table isn't a rate table but the time it takes to get to half of its strength and accounts for this slowdown. I use 12.5% chlorinating liquid and don't run into any problems even after a month or two which is about how long it takes me to go through 4 gallons, but the temp in storage is around 55-60F at night and 75-80F during the day.

Richard