A dialysis system includes a dialysis instrument; a disposable item configured to hold a dialysis fluid and including an at least substantially opaque portion and an at least substantially clear portion; at least one non-invasive temperature sensor mounted to the dialysis instrument so as to be pointed selectively at the at least substantially clear portion and the at least substantially opaque portion; and a processor configured to calculate a temperature of the dialysis fluid within the disposable item using (i) a first temperature measurement from the at least one sensor while pointed at the at least substantially opaque portion, and (ii) a second temperature measurement from the at least one sensor pointed at the at least substantially clear portion.