Can you re-use hydrogen peroxide? I want to keep a small, dark container of hydrogen peroxide in my bathroom to disinfect my toothbrush.?

Not sure what you mean by "re-use"

Are you putting some H.P. in a container, putting your brush in, then re-using that same peroxide?

Are you pouring the peroxide over the brush and saving the peroxide that you used for later?

No, to both of those situations.

A bottle of H.P. is very inexpensive.

Just use a new amount each time.

If you want to dispense some peroxide and then put the lid back on the unused stuff in the bottle, that's fine.

What do you mean "re-use"? You can open a bottle of peroxide and use it as needed...pour it into a small cup or something, but you can't use the same peroxide over and over.