Good morning to you bro, based on my experience with clownfishes last time,the moment you found out that your clown is infected with brook, immediately catch it out and give it a freshwater bath/dip. That will help in reducing/stop the slime from appearing again.
DO TAKE NOTE THAT CLOWNFISHES CANT TOLERATE BEING IN LOW SALINITY WATER OR FRESHWATER FOR TOO LONG.
You can try this method in future bro. Hopefully it does help!