diff --git a/gstools/covmodel/models.py b/gstools/covmodel/models.py
index a41415cc9..0e729a2c2 100644
--- a/gstools/covmodel/models.py
+++ b/gstools/covmodel/models.py
@@ -412,14 +412,14 @@ def default_opt_arg(self):
     def default_opt_arg_bounds(self):
         """Defaults for boundaries of the optional arguments.
 
-            * ``{"alpha": [0.5, inf]}``
+            * ``{"alpha": [0.5, 50.0]}``
 
         Returns
         -------
         :class:`dict`
             Boundaries for optional arguments
         """
-        return {"alpha": [0.5, np.inf]}
+        return {"alpha": [0.5, 50.0]}
 
     def cor(self, h):
         """Rational normalized correlation function."""
@@ -677,14 +677,14 @@ def default_opt_arg(self):
     def default_opt_arg_bounds(self):
         """Defaults for boundaries of the optional arguments.
 
-            * ``{"nu": [(dim-1)/2, inf, "co"]}``
+            * ``{"nu": [(dim-1)/2, 50.0, "co"]}``
 
         Returns
         -------
         :class:`dict`
             Boundaries for optional arguments
         """
-        return {"nu": [(self.dim - 1) / 2, np.inf, "co"]}
+        return {"nu": [(self.dim - 1) / 2, 50.0, "co"]}
 
     def cor(self, h):
         """Super-Spherical normalized correlation function."""
@@ -751,14 +751,14 @@ def default_opt_arg(self):
     def default_opt_arg_bounds(self):
         """Defaults for boundaries of the optional arguments.
 
-            * ``{"nu": [dim/2 - 1, inf, "co"]}``
+            * ``{"nu": [dim/2 - 1, 50.0, "co"]}``
 
         Returns
         -------
         :class:`dict`
             Boundaries for optional arguments
         """
-        return {"nu": [self.dim / 2 - 1, np.inf, "co"]}
+        return {"nu": [self.dim / 2 - 1, 50.0, "co"]}
 
     def check_opt_arg(self):
         """Check the optional arguments.
diff --git a/gstools/covmodel/tpl_models.py b/gstools/covmodel/tpl_models.py
index a097e888a..2f13a0e24 100644
--- a/gstools/covmodel/tpl_models.py
+++ b/gstools/covmodel/tpl_models.py
@@ -148,7 +148,7 @@ class TPLGaussian(TPLCovModel):
         Default: ``0.5``
     len_low : :class:`float`, optional
         The lower length scale truncation of the model.
-        Standard range: ``[0, 1000]``.
+        Standard range: ``[0, inf]``.
         Default: ``0.0``
     """
 
@@ -167,7 +167,7 @@ def default_opt_arg(self):
     def default_opt_arg_bounds(self):
         """Defaults for boundaries of the optional arguments.
 
-            * ``{"hurst": [0, 1, "oo"], "len_low": [0, 1000, "cc"]}``
+            * ``{"hurst": [0, 1, "oo"], "len_low": [0, inf, "cc"]}``
 
         Returns
         -------
@@ -275,7 +275,7 @@ class TPLExponential(TPLCovModel):
         Default: ``0.5``
     len_low : :class:`float`, optional
         The lower length scale truncation of the model.
-        Standard range: ``[0, 1000]``.
+        Standard range: ``[0, inf]``.
         Default: ``0.0``
     """
 
@@ -294,7 +294,7 @@ def default_opt_arg(self):
     def default_opt_arg_bounds(self):
         """Defaults for boundaries of the optional arguments.
 
-            * ``{"hurst": [0, 1, "oo"], "len_low": [0, 1000, "cc"]}``
+            * ``{"hurst": [0, 1, "oo"], "len_low": [0, inf, "cc"]}``
 
         Returns
         -------
@@ -413,7 +413,7 @@ class TPLStable(TPLCovModel):
         Default: ``1.5``
     len_low : :class:`float`, optional
         The lower length scale truncation of the model.
-        Standard range: ``[0, 1000]``.
+        Standard range: ``[0, inf]``.
         Default: ``0.0``
     """
 
@@ -434,7 +434,7 @@ def default_opt_arg_bounds(self):
 
             * ``{"hurst": [0, 1, "oo"],
               "alpha": [0, 2, "oc"],
-              "len_low": [0, 1000, "cc"]}``
+              "len_low": [0, inf, "cc"]}``
 
         Returns
         -------
@@ -459,7 +459,7 @@ def check_opt_arg(self):
         if self.alpha < 0.3:
             warnings.warn(
                 "TPLStable: parameter 'alpha' is < 0.3, "
-                + "count with unstable results",
+                "count with unstable results",
                 AttributeWarning,
             )
 
@@ -537,14 +537,14 @@ def default_opt_arg(self):
     def default_opt_arg_bounds(self):
         """Defaults for boundaries of the optional arguments.
 
-            * ``{"nu": [dim/2 - 1, inf, "co"]}``
+            * ``{"nu": [dim/2 - 1, 50.0, "co"]}``
 
         Returns
         -------
         :class:`dict`
             Boundaries for optional arguments
         """
-        return {"nu": [(self.dim + 1) / 2, np.inf, "co"]}
+        return {"nu": [(self.dim + 1) / 2, 50.0, "co"]}
 
     def cor(self, h):
         """TPL Simple - normalized correlation function."""