I spit blood after i use a certain mouth wash, what could be the problem?

Gum disease: Blood in your mouth is not normal and usually associated with some form of periodontal (gum) disease. It's highly unlikely it's actually caused by any mouth wash. More than likely it's related to your brushing (and hopefully) flossing. See a dentist asap for an evaluation and appropriate treatment.

Trauma: Most likely trauma to the gums from improper flossing or brushing technique. If it doesn't happen all the time , the mouthwash use is most likely coincidental. No rinses available to the public will cause bleeding in an otherwise healthy person--see your dentist to be sure! (p.S. The plax pictured here is useless--a waste of money--with marketing ; fda approval based on a single flawed study!).