Bromine to Chlorine change over

[LocksmithLouie]

How long can one expect DMH to hang around or does it never go away?

[PoolDoc]

I don't know; it's not something the bromine companies have wanted to study. It seems to be pretty persistent, but it may be biodegraded like cyanuric acid, if your pool gets well and truly 'swamped'. But there's no easy test for it, so it's not something I can investigate.