Bromine to Chlorine change over

[PoolDoc]

Yes, bromine can't be stabilized against sunlight . . . and the presence of bromide ions (used up bromine) prevents chlorine from being stabilized.

Drain as much as you can safely drain, and then refill. Bromide ions, in the absence of dimethyl hydantoin (DMH), will apparently be converted eventually to an inactive form, bromate. But the DMH apparently prevents this. See http://pool9.net/bromine/

If you used more than a few pounds of bromine, you should drain as far as you can, refill to 3x that depth (6" => 18") and drain again before final filling.

Sorry!

[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.