 The Effects of Patiromer on Serum Potassium Level and Gut Microbiome of ESRD Patients With Hyperkalemia potassium greater than 5 milliequivalents per liter is a non-randomized, crossover study. This is an open-label, pilot clinical trial with 3 sequential phases of a 2 weeks of no intervention, b 12 weeks of Patiromer treatment, and c 6 weeks of no intervention. Treatment with Patiromer will be initiated at a dose of 8.4 grams, once daily and observed for a week, then uptitrated to 16.8 grams once daily. Eligible study subjects will collect stool samples and provide blood and urine samples. 