The quick death sure confirms the brooklynella diagnosis by the folks above. Another sign of brook is the asymetrical "spots" that is common with ich. Once you've seen ich, its fairly easy to diagnose.
Brook presents in many different ways; but your other fish need formalin ASAP. (Or a product that contains formalin, like Quick Cure) Treatment must be done in a HT/QT. Clowns are very susceptible to this parasite and I'm just guessing that they were added recently and not quarantined. Sorry, if I'm wrong.