php - Codeigniter Execute model only once -

i have controller call model method minus-ing 2 tables. everytime controller access in browser, model func minus 2 table. want minus if other table have changes. how can that?

controller

function slots(){          $totalpaid911 = $this->data->participantpaid911();         $totalpaid1214 = $this->data->participantpaid1214();         $totalpaidkapihan = $this->data->participantpaidkapihan();          $paid = array('totalpaid911' => $totalpaid911,                       'totalpaid1214' => $totalpaid1214,                       'totalpaidkapihan' => $totalpaidkapihan);          $test = $this->data->updateslottotal911($paid);          $data['data'] = $this->data->slotstatus();          $this->load->view('site/header',$data);         $this->load->view('site/minicamp-slots',$data);         $this->load->view('site/login-modal');         $this->load->view('site/signup-modal');         $this->load->view('site/footer'); } 

model

function updateslottotal911($paid){     $this->db->select('slotavailable');     $this->db->where('program','9-11 mini camp');     $query = $this->db->get('tbl_slot_status');      $result = $query->result();      $slotavailable = $result['0']->slotavailable - $paid['totalpaid911'];       $data = array('slotavailable' => $slotavailable);      $this->db->where('program','9-11 mini camp');     $this->db->update('tbl_slot_status',$data);    } 

newbie in codeigniter here :(