FeCl dosing for P chemical precipitation

Hi,

I am building an ASM2dISS model and I added a dosing block to dose FeCl before the secondary clarifier. I've noticed that with or without it the TP in the effluent does not change.

Q_dose = 63 L/h; 
C_dose = 564 g/mc
P_eq = 1.5
Rho = 1410 g/mc
Strength = 40%

What would be the reason for this?

Thanks.