I know it's not spring, but I get what looks like that ever spring. This looks just like live oak pollen. Makes it way through the screen onto the pool surface every spring, clumps together in eraser size-dime-penny-quarter-half dollar size circles every year. Last for about a month. Come out in the morning, can be a 100 of them all over the surface. Love my AA in-floor cleaner. Runs the most at this time of year. I use hair nets in the skimmer, get a box of 100 for $5, have to change them every single day when the Oaks are doing their thing. I agree, looks like fine grass, pollen, etc.