I went a way for 2 months, leaving my tank in the care of my parents. Who did basicly nothing. When i came back i was appalled at the tanks condition.My substrate has a thick brownish/purpleish/redish layer on it, my glass has stringy brown scum on it, and my water is about 6 inches low. I dont have any fish in it yet. What do i do to get it back to normal.