hi i'm studying the potential of somme rhizobacteria to solubilize phosphate and producing AIA , and i want to study the potential of solubilizing potassium (KSB) so in many research they use the aleksandrov medium amended with insoluble source of potassium, so my question can you give me the name of a commercial product containing an insoluble form of potassium or any thing can help me in this study.