We model a suspension of weak ionic microgels as a suspension of ion-permeable soft colloids that can exchange microions with a reservoir at a constant salt concentration and pH value. Similar to previous works, the system is thus described within the semi-grand canonical ensemble, allowing for an exchange of microions but keeping the number of microgels fixed. Furthermore, we employ the spherical cell model approximation, 39 i.e. we consider only a single spherical microgel, centered in an overall electroneutral spherical cell of radius R.