The present invention relates to a method for optimizing the supply of a catalyst slurry during a polymerization process for preparing a polyolefin in a polymerization reactor (1), whereby said slurry consists of solid catalyst particles suspended in a hydrocarbon diluent and is characterised by a ratio of solid catalyst particles/diluent, whereby the catalyst slurry is fed to the reactor through at least two parallel catalyst feeding conduits (4, 104) which are intermittently operative in the polymerisation process, said method comprising the steps of : - determining an effective initial ratio solid catalyst particles/diluent for the polymerization process; - determining the actual ratio solid catalyst particles/diluent in a first operative feeding conduit (4); - calculating the difference between actual and initial ratio and in the event that said difference is more than a specified threshold, shutting down the first catalyst feeding conduit (4) and activating a second catalyst feeding conduit (104). The catalyst slurry is periodically supplied to the reactor. The invention also relates to polyolefin production processes and polyolefin producing units.