Hello and welcome to TFP! Looks like a good bunch of algae to me. Since you're new here, I'll simply point you to the "Vital Links" below in my signature. The "SLAM" link is how we remove algae. To do that, you'll need a TF-100 (Link below) or Taylor K-2006C test kit. But you'll need to look those over then get back with us if you have any specific questions about the products or how to conduct the SLAM. Thanks for using the forum.