It is the specific aim of this pilot study to assess the feasibility of achieving and maintaining a serum P less than or equal to 3.5 mg/dL (1.13 mmol/L) in patients with eGFR >20 and <45 mL/min with any of the 3 commercially available P lowering agents (calcium acetate, sevelamer carbonate, or lanthanum carbonate). Results of this study will clarify the degree of separation in serum P that can be achieved with the use of P lowering agents and the current standard of care (P binder initiation when P > 5.5 mg/dL or 1.78 mmol/L). Furthermore, this knowledge, combined with analyses of the secondary aims and outcomes of interest, will serve to facilitate the design of a properly powered, randomized, placebo controlled clinical outcomes trial that will firmly establish the necessity of achieving a specific target P in patients with CKD. The secondary aims of this pilot study are to provide insight into the optimal detection of progression of abnormalities in mineral metabolism and their relationship to vascular disease in CKD. The tertiary aim is to evaluate long term outcomes related to phosphorus normalization with respect to renal replacement therapy or death.