Hello we recently bought a home and it had a 21'X 41' Oval above ground pool. The pool doesn't seem to have been taken care of the best. It was not covered for winter and upon looking at it appears to have a reddish gunk all over the bottom of it. The pool is at least 3 years old according to the neighbors. What are my first steps? Should I drain and try to refill, or test the water and see if I can win the battle using SLAM?