Any chance you got a liner with a black/ dark gray and white bottom (sort of patterned with black/ gray 'stones' (not 'spots' - the 'stone' shapes are striated) - if so - you should see the water clear up as the level rises [something about the internal refraction of these liners makes the water look green when the water level is low ] If you have a pattern like this it's not algae - just physics