Hi I am going to purchase a tank and the people that are selling it, currently has it running as a salt water tank, i am going to use it for fresh water. I was wondering all the dirty stuff around it the tank, kind of like brown and yellow algaes im assuming. How can i clean that off, like what is the quickest way to do it? The owners of the tank told me to use a razor blade to scrape it off. Any ideas or proper ways to clean this? Thanks.