Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
CSM+B is not K2SO4.
Completely different materials.
CSM+B might also be called Plantex CSM+B. (I have also seen it called Nutritrace)
K2SO4 is a good source of potassium. (also provides sulfur). It is used if your tank has a reasonable source of nitrogen (perhaps fish food) and you do not want to dose a high level of KNO3. You can substitute K2SO4 so the tank still gets as much K (potassium) as it needs.
CSM+B is a trace mineral source. About a dozen elements, including boron.