There is clear stringy fungus or bacteria grwoing on my angelfish :o

My only viel angel fish started to get this clear stringy stuff hanging of his fins and tail. It looked as if his slime coat is creating it. Now 2 other angels are infected with this stuff so I whent out and bought Primafix, because its suposed to take care of fungus and bacteria. I used the primafix for 7 day and nothing has changed the stuff is still on thier fins. what do I do.