Just a suggestion...IF you have tried everything else found on this site, AND you have a cartridge filter, you may want to check your cartridges.

I had a similar problem about 8 years ago when I opened to a swamp--it was my filter cartridges. They just couldn't keep up with the enormous algae bloom I had that year. Of course, I probably helped destroy them with the amount of chlorine I had to use, along with the number of times I had to clean them--even after vacuuming to waste. We're talking SWAMP! The pool cleared very quickly after changing them.

A serious algae bloom is difficult to deal with, even if you don't have a cartridge filter. Mine originated from having a mesh safety cover. I love the fact that it's light weight and I don't have to pump water off of it in the winter, but the mesh lets in light and algae grows quickly here in the spring before opening. To alleviate this problem, I purchased a 'mesh mate' cover that floats on the pool water's surface--under the mesh safety cover. Since it's black, it blocks out the sunlight and eliminates algae growth. I open to a clean pool every spring now.

Hope this helps