Choose your substrate according your shrimp's need. Amazonia bring ph down to 6.4, Africana bring ph down to 5.9, Malaya brings ph down to 5.5.
My Amazonia brings my pH down under 6. I heard that the new Amazonia buffers around the same as Africana/ Malaya too? Anyway, a lot of people have had success with Amazonia but there are mixed reviews on FSS.