I can't pick just one thing that may have caused this as I had a few things going on. 2 of which were bought a nano Korillia, ran it for 2 days before deciding it was to much flow. Then a chemiclean treatment. Any ideas ?
It is likely a reaction to change, no biggie. Most likely you are going to get a split pretty soon, Duncans tend to get a little flat, or even fully closed right before they make new heads. At this point I wouldn't worry a bit. Duncans can take a fair amount of flow also, in fact I like that look better than a low flow Duncan.