That looks a lot like dinoflagellates. If so, water changes are not going to help, and may even feed it. .
I have something going on in my tank as well. I went almost 2years without any agae, and whamo. I got it everywhere. I am not 100% sure what type it is, but I am doing WC, and cutting way back on my feeding, re introduced a Sea hare, and hoping for the best.
I swear its something in the water