King British WS3 White Spot?

Hi i have a large 7x2x2 fishtank coldwater my goldfish have come into contect with slime. i was using Melafix and PimaFix when i was putting some new fish in for 3 days then afther that slime apper some of my fish now have slime my pnly problem is that will i have to put the carbon back into get rid of any Melafix and PimaFix in the water before using King British WS3 to treat the tank.i did today a 50% water change, and put in fish salts