Question about "Timeout reached"

The timeout has reached. The timeout has reached, But not retrieved from the poolConnection. This may occur because all pool connections are in use and the maximum pool size is reached.
Note: An unhandled exception occurs during the execution of the current Web request. Check the stack trace information to learn about this error and CodeDetailed information about the cause of the error.

Exception details: system. invalidoperationexception:The timeout has reached.The timeout has reached,But not retrieved from the poolConnection. This may occur because all pool connections are in use and the maximum pool size is reached.

At first, I thought it was the reason why the connection or datareader was not closed. Check all the code. I am afraid that the database connection has not been closed because sqlhelper is used. Some results are found. After processing, the results did not appear at the beginning. I'm glad to hear that it is really uncomfortable to let others see such a page. Besides, I am currently promoting it to colleges and universities.
Connectionstring, plus "Max pool size = 300 ". Haha, it has been running for a few days and there is no problem yet. OK!