When using unstable processing solutions, high recirculation and/or replenishment rates may be required. However, when replenisher is added to a processing tank, a noticeable drop in the temperature of the processing solution may occur. Such a drop in temperature may lead to variable photographic sensitometry of the material being processed. Described herein is apparatus in which temperature control means (28) are provided to ensure that the temperature of the solution being added to the processing tank does not produce such a temperature drop.