A Chelsea filter and dichroscope are completely different tools and you need both. Look on line you should be able to get both together for under 100 dollars. I would also recommend a UV light . You can pick one up at Lowes or Home Depot. A UV flashlight is more convienent to use. Also a regular flashlight positioned with the light stright up covered with a tissue can also be used to ID diffusion treated stones.
Hope this helps.