dosing ?

[donkey77]

Picked up a used doser with red sea a b c foundation powder, my par are
Ca 525-550
KH/alk 8.3 dkh
Mg 1550ppm
all done with salifert i know a little high, i will take readings for the next 4 days to see what my tank uses, its 100g system, i run carbon
Do i premix the powder into containers. How do i figure out how much iam setting the doser too