Examining the Impact of Using Two Dialysers in Parallel on Dialysis Adequacy in Hemodialysis Patients

Inclusion Criteria: * Age \> 18 years * Patients must be on a stable regimen of hemodialysis for ≥ 3 months ('stable' defined as not expected to require a change to the duration or frequency of treatments) * Serum phosphate \> 1.6 mmol/l on last two consecutive lab tests at least 3 weeks apart (KDOQI guidelines recommend maintaining predialysis phosphate \< 1.8mmol/l - as such, phosphate lowering in this subgroup of patients is particularly relevant) * Patients must be on stable doses of a phosphate binder with no changes in dose 1 month prior to study enrolment. * Blood flow rate ≥ 350 ml/min through a well-functioning access (This will exclude patients receiving inadequate dialysis due to a temporary venous dialysis catheter and will ensure sufficient blood flow to permit dialysis using two dialysers in parallel.) Exclusion Criteria: * Patients who have a scheduled renal transplant, change in dialysis modality, surgery or hospitalization or plan on moving away from the study site in the next three months. * Patients with a projected life expectancy of less than 3 months. * Patients with a contraindication to intra-dialytic anticoagulation. (Some patients require a small increase in the amount of anticoagulation required to prevent dialyser clotting when using two dialysers in parallel). * Patients who have missed \>8 dialysis treatments in the past 3 months. * Patients with a dialysis regimen of \>3 runs per week. * Failure to provide informed consent. * Patients enrolled in another (interventional) trial