The disclosed subject matter relates to extracorporeal blood processing or other processing of fluids. A blood treatment system treats blood with multiple fluids and performs fluid balancing on a patient's blood compartment. Multiple streams influence the patient temperature but only a subset of the fluids are dynamically temperature regulated. The system regulates a temperature of the flow, for example, of dialysate in order to regulate the return temperature of blood, in such a way that the temperature effect of the multiple streams is compensated.