It took almost 3 weeks to clear out the green soup in my pool after being covered all winter long. After I got the ph level down to around 7.4 and kept the chlorine levels in the 20s the water finally cleared up. Once the chlorine level dropped to around 4 ppm I put my solar cover back on. Now, after only 2 days the water is green again with algae growing on the pool walls. What's going on? Does the blue solar cover encourage algae growth or something?

Ph=7.5
Cya=48
FC=4.5