diff --git a/bfps/NavierStokes.py b/bfps/NavierStokes.py
index 9d0a770dfeb520a25e2e971c938df0a8c181fd6d..bee8d8a672330ee3287b94c03e09131a89f173a6 100644
--- a/bfps/NavierStokes.py
+++ b/bfps/NavierStokes.py
@@ -591,6 +591,49 @@ class NavierStokes(bfps.fluid_base.fluid_particle_base):
                          self.parameters['nz'],
                          self.parameters['nx']//2+1,
                          3))
+    def write_par(self, iter0 = 0):
+        super(NavierStokes, self).write_par(iter0 = iter0)
+        with h5py.File(os.path.join(self.work_dir, self.simname + '.h5'), 'r+') as ofile:
+            kspace = self.get_kspace()
+            nshells = kspace['nshell'].shape[0]
+            if self.QR_stats_on:
+                time_chunk = 2**20//(8*3*self.parameters['histogram_bins'])
+                time_chunk = max(time_chunk, 1)
+                ofile.create_dataset('statistics/histograms/trS2_Q_R',
+                                     (1,
+                                      self.parameters['histogram_bins'],
+                                      3),
+                                     chunks = (time_chunk,
+                                               self.parameters['histogram_bins'],
+                                               3),
+                                     maxshape = (None,
+                                                 self.parameters['histogram_bins'],
+                                                 3),
+                                     dtype = np.int64,
+                                     compression = 'gzip')
+                time_chunk = 2**20//(8*3*10)
+                time_chunk = max(time_chunk, 1)
+                a = ofile.create_dataset('statistics/moments/trS2_Q_R',
+                                     (1, 10, 3),
+                                     chunks = (time_chunk, 10, 3),
+                                     maxshape = (None, 10, 3),
+                                     dtype = np.float64,
+                                     compression = 'gzip')
+                time_chunk = 2**20//(8*self.parameters['QR2D_histogram_bins']**2)
+                time_chunk = max(time_chunk, 1)
+                ofile.create_dataset('statistics/histograms/QR2D',
+                                     (1,
+                                      self.parameters['QR2D_histogram_bins'],
+                                      self.parameters['QR2D_histogram_bins']),
+                                     chunks = (time_chunk,
+                                               self.parameters['QR2D_histogram_bins'],
+                                               self.parameters['QR2D_histogram_bins']),
+                                     maxshape = (None,
+                                                 self.parameters['QR2D_histogram_bins'],
+                                                 self.parameters['QR2D_histogram_bins']),
+                                     dtype = np.int64,
+                                     compression = 'gzip')
+        return None
 
 def launch(
         opt,
diff --git a/bfps/fluid_base.py b/bfps/fluid_base.py
index f29e99e5f846188085c4a9e5c84cc7d056c4a9b2..4d1d390cbd63b3732625bbbb22505c05f8b3dbcc 100644
--- a/bfps/fluid_base.py
+++ b/bfps/fluid_base.py
@@ -398,43 +398,6 @@ class fluid_particle_base(bfps.code):
             for k in kspace.keys():
                 ofile['kspace/' + k] = kspace[k]
             nshells = kspace['nshell'].shape[0]
-            if self.QR_stats_on:
-                time_chunk = 2**20//(8*3*self.parameters['histogram_bins'])
-                time_chunk = max(time_chunk, 1)
-                ofile.create_dataset('statistics/histograms/trS2_Q_R',
-                                     (1,
-                                      self.parameters['histogram_bins'],
-                                      3),
-                                     chunks = (time_chunk,
-                                               self.parameters['histogram_bins'],
-                                               3),
-                                     maxshape = (None,
-                                                 self.parameters['histogram_bins'],
-                                                 3),
-                                     dtype = np.int64,
-                                     compression = 'gzip')
-                time_chunk = 2**20//(8*3*10)
-                time_chunk = max(time_chunk, 1)
-                a = ofile.create_dataset('statistics/moments/trS2_Q_R',
-                                     (1, 10, 3),
-                                     chunks = (time_chunk, 10, 3),
-                                     maxshape = (None, 10, 3),
-                                     dtype = np.float64,
-                                     compression = 'gzip')
-                time_chunk = 2**20//(8*self.parameters['QR2D_histogram_bins']**2)
-                time_chunk = max(time_chunk, 1)
-                ofile.create_dataset('statistics/histograms/QR2D',
-                                     (1,
-                                      self.parameters['QR2D_histogram_bins'],
-                                      self.parameters['QR2D_histogram_bins']),
-                                     chunks = (time_chunk,
-                                               self.parameters['QR2D_histogram_bins'],
-                                               self.parameters['QR2D_histogram_bins']),
-                                     maxshape = (None,
-                                                 self.parameters['QR2D_histogram_bins'],
-                                                 self.parameters['QR2D_histogram_bins']),
-                                     dtype = np.int64,
-                                     compression = 'gzip')
             for k in ['velocity', 'vorticity']:
                 time_chunk = 2**20//(8*3*self.parameters['nx'])
                 time_chunk = max(time_chunk, 1)
diff --git a/tests/test_base.py b/tests/test_base.py
index 50a9820ab2917a1ce2f55385ca0751eabc4404cb..97632bb7dc2ab6ea2d6c7c663742b4c669a51b56 100755
--- a/tests/test_base.py
+++ b/tests/test_base.py
@@ -124,7 +124,9 @@ def launch(
     if opt.run:
         if opt.iteration == 0 and opt.initialize:
             if type(vorticity_field) == type(None):
-                c.generate_vector_field(write_to_file = True, spectra_slope = 1.5)
+                c.generate_vector_field(write_to_file = True,
+                                        spectra_slope = 2.0,
+                                        amplitude = 0.25)
             else:
                 vorticity_field.tofile(
                         os.path.join(c.work_dir,
diff --git a/tox_convergence.ini b/tox_convergence.ini
index a0123d4a011508ae6a25e5a7cd22d77e97241f48..447e32fe9a7ffa2fc7adbcd9e07ca464785b8700 100644
--- a/tox_convergence.ini
+++ b/tox_convergence.ini
@@ -14,7 +14,7 @@ commands =
         --run \
         --initialize \
         --ncpu 2 \
-        --nparticles 32 \
+        --nparticles 1 \
         --niter_todo 16 \
         --precision single \
         --wd "data/single"
@@ -23,7 +23,7 @@ commands =
         --run \
         --initialize \
         --ncpu 2 \
-        --nparticles 32 \
+        --nparticles 1 \
         --niter_todo 16 \
         --precision double \
         --wd "data/double"