Citric Acid is a poor chelaing agent. This means that 1 mole of CA does not complex with 1 mole of Ca++.

Now, assuming that 1 mole of Ca++ = 1 mole of CA, then your figures are ok, but you need an excess. If you look at the sequestrant levels in most developers, you find that it is about 2 - 5 g/l for strong sequestrants.