A hemodialysis system comprising: an arterial blood line for connecting to a patient's artery for collecting blood from a patient; a venous blood line for connecting to a patient's vein for returning blood to a patient; a dialyzer; a closed loop blood flow path which connects to said arterial blood line and said venous blood line for transporting blood from a patient to said dialyzer and back to a patient; a blood pump for pumping blood through said blood flow path; a first reservoir for storing a dialysate solution, said first reservoir having an inlet and an outlet; a second reservoir for storing a dialysate solution, said second reservoir having an inlet and an outlet; a closed loop dialysate flow path, isolated from the blood flow path, for transporting a dialysate either from said first reservoir to said dialyzer and back to said first reservoir, or from said second reservoir to said dialyzer and back to said second reservoir, said dialysate flow path including a first reservoir flow path connecting said first reservoir inlet and said first reservoir outlet to said dialysate flow path, and said dialysate flow path including a second reservoir flow path connecting said second reservoir inlet and said second reservoir outlet to said dialysate flow path, at least one dialysate pump for pumping dialysate through said dialysate flow path; a first reservoir fluid valve assembly configured to permit the flow of dialysate through said first reservoir flow path when open or to obstruct the flow of dialysate through said first reservoir flow path when closed; a second reservoir fluid valve assembly configured to permit the flow of dialysate through said second reservoir flow path when open or to obstruct the flow of dialysate through said second reservoir flow path when closed; and a processor connected to said first reservoir fluid valve assembly and said second reservoir fluid valve assembly, said processor programmed to selectively alternate between, 1) the opening of said first fluid valve assembly to permit the flow of dialysate through said first reservoir flow path while closing said second fluid valve assembly to obstruct the flow of dialysate through said second reservoir flow path, and 2) the closing of said first fluid valve assembly to obstruct the flow of dialysate through said first reservoir flow path while opening said second fluid valve assembly to permit the flow of dialysate through said second reservoir flow path. an arterial blood line for connecting to a patient's artery for collecting blood from a patient; a venous blood line for connecting to a patient's vein for returning blood to a patient; a dialyzer; a closed loop blood flow path which connects to said arterial blood line and said venous blood line for transporting blood from a patient to said dialyzer and back to a patient; a blood pump for pumping blood through said blood flow path; a first reservoir for storing a dialysate solution, said first reservoir having an inlet and an outlet; a second reservoir for storing a dialysate solution, said second reservoir having an inlet and an outlet; a closed loop dialysate flow path, isolated from the blood flow path, for transporting a dialysate either from said first reservoir to said dialyzer and back to said first reservoir, or from said second reservoir to said dialyzer and back to said second reservoir, said dialysate flow path including a first reservoir flow path connecting said first reservoir inlet and said first reservoir outlet to said dialysate flow path, and said dialysate flow path including a second reservoir flow path connecting said second reservoir inlet and said second reservoir outlet to said dialysate flow path, at least one dialysate pump for pumping dialysate through said dialysate flow path; a first reservoir fluid valve assembly configured to permit the flow of dialysate through said first reservoir flow path when open or to obstruct the flow of dialysate through said first reservoir flow path when closed; a second reservoir fluid valve assembly configured to permit the flow of dialysate through said second reservoir flow path when open or to obstruct the flow of dialysate through said second reservoir flow path when closed; and a processor connected to said first reservoir fluid valve assembly and said second reservoir fluid valve assembly, said processor programmed to selectively alternate between, 1) the opening of said first fluid valve assembly to permit the flow of dialysate through said first reservoir flow path while closing said second fluid valve assembly to obstruct the flow of dialysate through said second reservoir flow path, and 2) the closing of said first fluid valve assembly to obstruct the flow of dialysate through said first reservoir flow path while opening said second fluid valve assembly to permit the flow of dialysate through said second reservoir flow path.