Soak paper towells really well in white vinegar. plaster the inside of the tank with it and let it sit for a few hours or overnight. Then (it should still be wet) get a razor blade and scrape it clean. My 150 was a disaster when I got it from the previous owner over two years ago. Came out looking like new. Besides, do you really want traces of muratic acid? Do you want to expose your epoxy to that stuff? Just my two cents...