IS MY RED EARED SLIDER TURTLE SICK AGAIN?

i have a juvenile turtle and he had a respiratory infection in the past. Took him to the vet..got everything taken care of and he looks super healthy now! But lately his water has been looking really thick and kinda like.. Flakey on the surface.. I have a zoomed filter that works great and always has so i know thats not it... Has anyone else experienced this before?