Hundreds of Running / Terminated threads a minute - postgresql

Question

I'm using PostgreSQL 9.5 and Npgsql 2.2.5.0 to connect from an ASP.NET web service written with VB.NET to the PostgreSQL server.
The webservice gets around 15 requests a second.
The connection string I use is:
<connectionStrings>
<add name="PostgreConnectionStringPCMRead"
connectionString="Server=xxx.xxx.xxx.xxx;Port=5432;User
Id=the_user;Password=the_password;Database=example;
CommandTimeout=600;Timeout=30;ConnectionLifeTime=30;
Pooling=False;"/>
</connectionStrings>
When I take a look at the Windows Resource Monitor, I see hundreds of Terminated connections.
I realise that I am using Pooling=False, however when I set Pooling=True, I get errors "Timeout while getting a connection from pool."
With every query I use the following Class (I've left in only the essential code):
Public Class dlNpgSQL
Dim _sqlCommand As NpgsqlCommand
Dim _sqlDataAdapter As NpgsqlDataAdapter
Dim _dataset As DataSet
Public Sub New()
_sqlConnection = New NpgsqlConnection(ConfigurationManager.
ConnectionStrings("connstring").ConnectionString)
End Sub
Public Function GetDataSet(ByVal strQuery As String) As DataSet
_dataset = New DataSet
_sqlDataAdapter = New NpgsqlDataAdapter(strQuery, OpenConnection)
_sqlDataAdapter.Fill(_dataset)
Return _dataset
End Function
Public Function OpenConnection() As NpgsqlConnection
If _sqlConnection.State = ConnectionState.Closed Then
_sqlConnection.Open()
End If
End Function
Public Sub CloseConnection()
If _sqlConnection.State = ConnectionState.Open Then
_sqlConnection.Close()
End If
End Function
End Class
And then the actual query:
Dim ds As DataSet
Dim objDBRead As New dlNpgSQL("connstring")
tmpSQL = "SELECT * FROM table1"
ds = objDBRead.GetDataSet(tmpSQL)
If (objDBRead IsNot Nothing) Then
objDBRead.CloseConnection()
End If
So obviously, I'm opening and closing the connection with each query.
Is this the correct way to do things?
Should I be using pooling, and if yes, why am I getting the errors and how can I fix the issue?
Thanks!