diff --git a/ms2pip/core.py b/ms2pip/core.py
index 3ffd82b..fe50112 100644
--- a/ms2pip/core.py
+++ b/ms2pip/core.py
@@ -189,18 +189,34 @@ def predict_library(
         raise ValueError("Either `fasta_file` or `config` must be provided.")
 
     search_space = ProteomeSearchSpace.from_any(config)
-    search_space.build()
+    search_space.build(processes=processes)
+
+    # Convert to PSMList
+    psm_list = search_space.to_psm_list()
+
+    # Filter PSMs by mz
+    # TODO: Parallelize this step?
+    psm_list_filtered = search_space.filter_psms_by_mz(psm_list)
+
+    # Add retention time and ion mobility predictions
+    if add_retention_time:
+        logger.info("Adding retention time predictions...")
+        rt_predictor = RetentionTime(processes=processes)
+        rt_predictor.add_rt_predictions(psm_list_filtered)
+    if add_ion_mobility:
+        logger.info("Adding ion mobility predictions...")
+        im_predictor = IonMobility(processes=processes)
+        im_predictor.add_im_predictions(psm_list_filtered)
 
     for batch in track(
-        _into_batches(search_space, batch_size=batch_size),
+        _into_batches(psm_list_filtered, batch_size=batch_size),
         description="Predicting spectra...",
         total=ceil(len(search_space) / batch_size),
     ):
+
         logging.disable(logging.CRITICAL)
         yield predict_batch(
-            search_space.filter_psms_by_mz(PSMList(psm_list=list(batch))),
-            add_retention_time=add_retention_time,
-            add_ion_mobility=add_ion_mobility,
+            batch,
             model=model,
             model_dir=model_dir,
             processes=processes,
diff --git a/ms2pip/search_space.py b/ms2pip/search_space.py
index 2ac3a87..e969c53 100644
--- a/ms2pip/search_space.py
+++ b/ms2pip/search_space.py
@@ -265,7 +265,9 @@ def build(self, processes: int = 1):
             Number of processes to use for parallelization.
 
         """
-        processes = processes if processes else multiprocessing.cpu_count()
+        processes = (
+            processes if processes else multiprocessing.cpu_count()
+        )  # Always ignored because of the default value
         self._digest_fasta(processes)
         self._remove_redundancy()
         self._add_modifications(processes)
@@ -308,6 +310,10 @@ def filter_psms_by_mz(self, psms: PSMList) -> PSMList:
             ]
         )
 
+    def to_psm_list(self) -> PSMList:
+        """Convert search space to PSMList."""
+        return PSMList(psm_list=list(self))
+
     def _digest_fasta(self, processes: int = 1):
         """Digest FASTA file to peptides and populate search space."""
         # Convert to string to avoid issues with Path objects