Hm, I see here that that product has an active ingriedient of malachite green. That could definitely stress your fish out.
Malachite Green's toxicity is temperature and pH dependent, being more toxic with rising temperature and lower pH. One surprising item re Malachite use is its inactivation (oxidation) with exposure to light. Malachite Green treated systems should have their lights turned off. I have rarely seen this mentioned with product labels or inserts.
Malachite Green should be utilized in a separate treatment tank as it is quickly absorbed by detritus, natural gravels... most all plastics.
Unfortunately, Malachite Green is suspected of being a carcinogen as well as teratogen (a chemical that can alter DNA make-up), and respiratory poison. It is NOT to be used lightly (Fenner).