Blonde barbs being...what kind, exactly? Gold barbs? Albino tiger barbs? It would help to know exactly what kind of barbs and how many there are to reason out their aggression. How long have the barbs been in the tank? I know that some barbs can become territorial and nippy if they aren't kept in proper schools (usually six of more). My tiger barbs decided that they didn't like one of the oto cats I added to their tank last night and chased it all over the tank as a school (they've NEVER shown any aggression before and were even terrified of one of my cories), and there's seven of them, so they're in a proper school.