An apparatus for peritoneal dialysis comprising: an automated peritoneal dialysis cycler programmed to run a treatment session including a plurality of cycles, each cycle including a fill phase, a dwell phase, and a drain phase of a peritoneal cavity of a patient, the treatment session lasting at most 720 min, the cycler having: a patient line configured to be placed in communication with the peritoneal cavity of the patient; at least a source of treatment fluid which includes an osmotic agent; and at least one pump to circulate the treatment fluid to be delivered to the patient through said patient line; and a control system configured to drive said cycler to deliver the treatment fluid, wherein, during the same treatment session, the control system is programmed to: run a fill phase of a first cycle delivering a first treatment fluid to the patient, the first treatment fluid having a first concentration of the osmotic agent; subsequently to the first cycle, run a fill phase of a second cycle delivering a second treatment fluid to the patient, the second treatment fluid having a second concentration of the osmotic agent different from the concentration of the first treatment fluid; and subsequently to the second cycle, run a fill phase of a third cycle delivering a third treatment fluid to the patient, the third treatment fluid having a third concentration of the osmotic agent different from the concentration of the second treatment fluid, wherein the second concentration of the osmotic agent is lower than the first concentration of the osmotic agent and the third concentration of osmotic agent is higher than the second concentration of osmotic agent, or wherein the second concentration of the osmotic agent is higher than the first concentration of the osmotic agent and the third concentration of osmotic agent is lower than the second concentration of osmotic agent. an automated peritoneal dialysis cycler programmed to run a treatment session including a plurality of cycles, each cycle including a fill phase, a dwell phase, and a drain phase of a peritoneal cavity of a patient, the treatment session lasting at most 720 min, the cycler having: a patient line configured to be placed in communication with the peritoneal cavity of the patient; at least a source of treatment fluid which includes an osmotic agent; and at least one pump to circulate the treatment fluid to be delivered to the patient through said patient line; and a patient line configured to be placed in communication with the peritoneal cavity of the patient; at least a source of treatment fluid which includes an osmotic agent; and at least one pump to circulate the treatment fluid to be delivered to the patient through said patient line; and a control system configured to drive said cycler to deliver the treatment fluid, wherein, during the same treatment session, the control system is programmed to: run a fill phase of a first cycle delivering a first treatment fluid to the patient, the first treatment fluid having a first concentration of the osmotic agent; subsequently to the first cycle, run a fill phase of a second cycle delivering a second treatment fluid to the patient, the second treatment fluid having a second concentration of the osmotic agent different from the concentration of the first treatment fluid; and subsequently to the second cycle, run a fill phase of a third cycle delivering a third treatment fluid to the patient, the third treatment fluid having a third concentration of the osmotic agent different from the concentration of the second treatment fluid, wherein the second concentration of the osmotic agent is lower than the first concentration of the osmotic agent and the third concentration of osmotic agent is higher than the second concentration of osmotic agent, or wherein the second concentration of the osmotic agent is higher than the first concentration of the osmotic agent and the third concentration of osmotic agent is lower than the second concentration of osmotic agent. run a fill phase of a first cycle delivering a first treatment fluid to the patient, the first treatment fluid having a first concentration of the osmotic agent; subsequently to the first cycle, run a fill phase of a second cycle delivering a second treatment fluid to the patient, the second treatment fluid having a second concentration of the osmotic agent different from the concentration of the first treatment fluid; and subsequently to the second cycle, run a fill phase of a third cycle delivering a third treatment fluid to the patient, the third treatment fluid having a third concentration of the osmotic agent different from the concentration of the second treatment fluid, wherein the second concentration of the osmotic agent is lower than the first concentration of the osmotic agent and the third concentration of osmotic agent is higher than the second concentration of osmotic agent, or wherein the second concentration of the osmotic agent is higher than the first concentration of the osmotic agent and the third concentration of osmotic agent is lower than the second concentration of osmotic agent.