npgsql preferred connection pooling usage

Question

I've been noticing connection pool being exhausted...I dont get full blown exception because its happening behind web app... but basically

Npgsql.NpgsqlConnectorPool.RequestCOnnector(Npgsql.MpgsqlConnection)

My web app basically breaks, and fails to create any new connections. If I restart web app server, or database engine, things start to work again for a short time. My connectionstring specifies min 15 connections in the pool, 30 max.

My question is in the context of a web application I should be able to just get a connection

using(var connection = new NpgsqlConnection(connectionstring)){
    connection.open(); 
    dostuff();
}

Am I doing something wrong? Disabling pooling ends up working, and performing well, but seems like the wrong way to solve this problem.