This is such a hard topic because there can be so many factors in a rat's environment that can cause sneezing (bedding, perfumes, air fresheners, dust, etc) so it is hard to pinpoint. Good that you have them on meds for their sneezing but if it is still there and not completely gone, well that is a hard one. Rats are so sensitive with their respiratory systems so little things can set them off. Could there be any mold issues from the dampness caused by spraying down the Carefresh? Just thinking out loud here. I am sure you will get some good advice on this forum once others see your post. Sounds like you are trying very hard to get this figured out. I feel for you!