Hi, i am new to the forum. I have read lots of great info so far. Our above ground pool keeps getting a green algae. My chlorine level is 3 and the pH is 7.5. I shocked with liquid chlorine last night and brushed the entire pool. This morning it is very milky and there is of course greenish yellow residue on bottom. My question is do I vacuum to waste now and backwash my filter? How long does it take to clear? I keep getting to this point and then it turns green again! Help please!