Developing a Chat Application using C# in ASP.Net

Question

Hi,
i am building a Multi -User Chat Application using c# in ASP.Net
for the first 15 mins with 5-8 users it works fine
but after 15mins with more users andf more messages it becomes slow
i am using the ArrayList() to store the user messages, and the all messasges from the ArrayList are displayed on a webform using a RemoteScript function()
so every time the page is refreshed the RemoteScript function retriebves all the elements from the ArrayList and display them on the webpage

so can u help me, is it the right approach to do it.