I went and purchased some new koi from supposedly a reputable dealer but when I put them in with my fish , my fish started acting sluggesh, I ended up loosing 5 of my fish I had to start with and 2 of the new one, I finally have away the new fish and my fish are finally a ting right again, any ideas what went so wrong? Parasites, maybe? I told the man I got them from of course he said he hadn't had any complaints, this happened with in a couple of hours they started acting strange and over the course of a couple of days I lost the fish.Help