A blood treatment apparatus with - a hydraulic system comprising at least one first filtration stage and one second filtration stage, comprising at least one conveying apparatus (11, 12, 31), at least one flow limitation device (Vdia, Vsub, 21) or a flow divider valve, as well as comprising at least one dialysis liquid supply line and at least one substituate line, as well as optionally at least one branch line which connects the dialysis liquid supply line and the substituate line; - a medical functional apparatus embodied as blood cassette comprising a substituate line and a substituate port as well as a blood conducting-line which is part of an extracorporeal blood circuit, wherein the substituate port is provided to receive substituate produced by the hydraulic system of the blood treatment apparatus, wherein the medical functional apparatus does not comprise any apparatus which is arranged and/or provided for dosing the substituate passing over from the substituate line into a blood-conducting line of the blood cassette; and - a control or regulating apparatus, configured or programmed to execute a method for dosing, creating or providing a substituate which was produced by a blood treatment apparatus, wherein dosing takes place by the hydraulic system of the blood treatment apparatus; wherein the method comprises the steps: - conveying a first fluid through the first filtration stage into the dialysis liquid supply line, producing or generating a dialysis liquid which is introducible into the dialyzer; - conducting a portion of the dialysis liquid into a substituate line which attaches to the second filtration stage or is in fluid communication with it, producing or generating a substituate which is introducible into an extracorporeal blood circuit when the dialysate passes through the second filtration stage; and - regulating or controlling the size of the portion of the dialysis liquid which passes through the second filtration stage, or of the portion which after filtration at the second filtration stage is provided to be introduced into the blood cassette via the substituate line, wherein regulating or controlling takes place by affecting at least one conveying apparatus (11, 12, 31), at least one flow limitation device (Vdia, Vsub, 21) or a flow divider valve, which are each present in the dialysis liquid supply line and/or in the substituate line and/or in the branch line which connects the dialysis liquid supply line and the substituate line or affect these. - a hydraulic system comprising at least one first filtration stage and one second filtration stage, comprising at least one conveying apparatus (11, 12, 31), at least one flow limitation device (Vdia, Vsub, 21) or a flow divider valve, as well as comprising at least one dialysis liquid supply line and at least one substituate line, as well as optionally at least one branch line which connects the dialysis liquid supply line and the substituate line; - a medical functional apparatus embodied as blood cassette comprising a substituate line and a substituate port as well as a blood conducting-line which is part of an extracorporeal blood circuit, wherein the substituate port is provided to receive substituate produced by the hydraulic system of the blood treatment apparatus, wherein the medical functional apparatus does not comprise any apparatus which is arranged and/or provided for dosing the substituate passing over from the substituate line into a blood-conducting line of the blood cassette; and - a control or regulating apparatus, configured or programmed to execute a method for dosing, creating or providing a substituate which was produced by a blood treatment apparatus, wherein dosing takes place by the hydraulic system of the blood treatment apparatus; - conveying a first fluid through the first filtration stage into the dialysis liquid supply line, producing or generating a dialysis liquid which is introducible into the dialyzer; - conducting a portion of the dialysis liquid into a substituate line which attaches to the second filtration stage or is in fluid communication with it, producing or generating a substituate which is introducible into an extracorporeal blood circuit when the dialysate passes through the second filtration stage; and - regulating or controlling the size of the portion of the dialysis liquid which passes through the second filtration stage, or of the portion which after filtration at the second filtration stage is provided to be introduced into the blood cassette via the substituate line, wherein regulating or controlling takes place by affecting at least one conveying apparatus (11, 12, 31), at least one flow limitation device (Vdia, Vsub, 21) or a flow divider valve, which are each present in the dialysis liquid supply line and/or in the substituate line and/or in the branch line which connects the dialysis liquid supply line and the substituate line or affect these.