From your (above) link....
DO NOT STORE AT TEMPERATURES ABOVE: 52 Deg.C (125 Deg.F)
Storage above this temperature may result in rapid decomposition,
evolution of chlorine gas and heat sufficient to ignite combustible
products.
HTH is used everyday when a repair crew fixes a broken water main/pipe, they toss in a handful and re-join the pipe.
For a non-trained citizen, its pretty easy to over-treat water. The link did a good job with a basic “preper” explanation.