Well the more
EPA the better, so if you want more
EPA then yes buy a different one, I am not 100% sure
how you tell if it has Mercury in it or not, maybe in should say on the bottle, but i guess it might not sure. I buy Usana fish oil and i know its a good brand and does take the Mercury out, my suppler has told me it does. It also contains vitamin D as it is needed to absorb the fish oil properly. Now how long it takes to work is different to everyone and depends on the issue etc.