Last spring using a mesh safety cover for the first time, we opened to a neon green pool. What a mess and not wanting to go through that again, I bought a "cover-mate" which is a black heavy-duty cover that is just like a solar cover except it's solid and doesn't let light go into the water. This cover floats on the water under the mesh cover. We opened the pool today (it was closed in the end of September here in CT) and no algae except for a small amount on the top step where there was a gap that let light through. The water was slightly murky but I'll take that any day over the green monster from last year.