Emittance preservation in the beam delivery system (BDS) is one of the major challenges in the Compact Linear Collider (CLIC). The fast detuning of the final focus optics requires an on-line tuning procedure in order to keep luminosity close to the maximum. In this paper we discuss different tuning techniques to mitigate the displacement of magnets in the CLIC BDS and in particular in the final focus system. Some of them require a fast luminosity measurement. Here we study the possibility to use beam-beam background processes at CLIC 3 TeV c.m. energy as a fast luminosity signal. In particular, the hadron multiplicity in the detector region is investigated.