My pool liner has a very dark mold on the underside which shows through the liner and looks bad. My pool service says that is what the numerous dark spots are. Is there anything to get rid of them. I use the Caribbean Clear system and when I use extra bleach it helps to lighten them but it isn't possible to continually use extra bleach in the pool. My pool service also suggested placing sulfur around the edge of the pool, hosing it in and with rain the sulfur would dissolve into the edge of the liner and help to kill this "mold." It did not work and is twice as bad this summer. I need help. The liner is only 4 years old and otherwise in excellent condition.