diff --git a/src/helpers.py b/src/helpers.py
index 22ee8a9..c204d12 100644
--- a/src/helpers.py
+++ b/src/helpers.py
@@ -6,8 +6,6 @@ def next_smaller(lst):
     last_item = None
     i = 0
     for index, item in enumerate(lst):
-        if item == 0:
-            break
         if last_item is None or (item >= last_item and index == i):
             last_item = item
             i += 1
@@ -15,11 +13,23 @@ def next_smaller(lst):
 
 
 def valid_pka_values(values):
+    """
+    This function filters possible pKa values for the app web page.
+    It's perfectly fine negative pKa values and non-sorted values in real life
+    but is not so usual. Then, for educational purposes, it was decided to
+    create this filter.
+
+    Parameters
+    ----------
+    values : tuple
+
+    Returns
+    -------
+    list
+
+    """
     values = list(values)
-    result = []
-    if values[0] == 0:
-        pass
-    elif is_sorted(values):
+    if is_sorted(values):
         result = values
     else:
         result = list(next_smaller(values))
diff --git a/tests/test_valid_pka_values.py b/tests/test_valid_pka_values.py
index 958fb0a..44ae70e 100644
--- a/tests/test_valid_pka_values.py
+++ b/tests/test_valid_pka_values.py
@@ -1,8 +1,8 @@
 from src.helpers import valid_pka_values
 
 
-def test_three_inputs_no_pka():
-    assert valid_pka_values((0, 0, 0)) == []
+def test_three_zero_inputs_three_pka():
+    assert valid_pka_values((0, 0, 0)) == [0, 0, 0]
 
 
 def test_three_inputs_one_pka():
@@ -21,14 +21,18 @@ def test_three_inputs_equal():
     assert valid_pka_values((1, 1, 1)) == [1, 1, 1]
 
 
-def test_four_inputs_no_pka():
-    assert valid_pka_values((0, 0, 0, 0)) == []
+def test_four_zero_inputs_four_pka():
+    assert valid_pka_values((0, 0, 0, 0)) == [0, 0, 0, 0]
 
 
 def test_three_inputs_sorted():
     assert valid_pka_values((1, 2, 3)) == [1, 2, 3]
 
 
+def test_three_inputs_sorted_first_zero():
+    assert valid_pka_values((0, 2, 3)) == [0, 2, 3]
+
+
 def test_three_inputs_sorted_two_equal():
     assert valid_pka_values((1, 2, 2)) == [1, 2, 2]