When I opened my pool last week (21 x 48 lined above ground) the water was a nasty green , and you couldn't see the bottom. I had the water tested and added the reccomended chemicals. I was told to use 4 bags of shock. After the filter ran for a few hours the green has turned to a brown. Is this the dead algae, and am I going to probably need to flock it to be able to vaccum it all out? Thanks