How to ensure fish is free of parasite after treatment

here is my situaution, I had an outbreak of Brooklynella and lost many fish. i did however manage to save a sailfin tang and a green chromis that I treated with quick cure. They have been in a QT for 8 weeks now with no signs of the parasite. The tang was showing signs when I started treatment but the Green Chromis never did show signs. I know the preferred treatment is formalin but only was able to get the Quick Cure at the time which has a much lowere dose of formalin in it. Could it be possible that the tang and Green Chromis still have the parasite after all this time with no signs and still be a carrier? I am so scared that I will be back where I started from when I started adding new fish again. Or do you think 8 weeks in a smaller tank would cause enough stress that they should have showed signs of it by now? THey both look great

 

I think you have made a wise choice by QTing for 8 weeks. It is extremely unlikely that they are carrying parasites at this point.