I'm in the process of lowering my TA, so I stopped at Leslie's Pool Store. Here in Tucson they have the lowest price on 31% MA, a two gallon box for $11.49. So I asked for three boxes (this will likely be my only chemical purchase for the year). Clerk says "that's a lot of acid to buy at once", I replied that it would likely last the whole season. He tells me that it will degrade and that I shouldn't store any acid. I replied that it isn't like I'm stocking up on liquid chlorine. He then informs me that acid loses it strength faster than liquid chlorine.
I asked him to explain the chemical process that causes it to degrade so fast. Just then our conversation was interrupted by him getting a phone call. As I'm leaving the store, I hear him telling the customer on the phone "Sorry to tell you this Mr. Xxxx, but it's time to drain that pool."
Pool store business as usual, sell lots of magic potions for lots of $$$, then when the pool has too much of XY or Z from the potions, time to drain and start over.