I did some searches for you; it seems that Protozin isn't commonly sold in the US so many of us may not be familiar with it. does it say anything in the leaflet or on the bottle? I'd do a water change anyway; you'll have to do one eventually to replenish water and keep nitrates down, so I wouldn't think it should harm anything. I also read the medications in it can disrupt your biofilter so I would do water tests every day to ensure that ammonia and nitrite are staying at 0.