Used a brass check valve, didn't go well.

[Aquattro]

Unfortunately if you cot enough copper in there to kill everything, it's likely leached into all your substrate. It won't get in the glass and gear, that can all be cleaned, but whether or not you can re-use the rock and sand, hard to say.
Use some of the media mentioned, then test with a couple of inverts and see if they survive. I wouldn't expect a brass valve to do that much damage in a week, but who knows.