I was hoping someone could ID this stuff. My trates and phates are (supposedly) 0 and PH is 8.2. It almost looks like string or twine but its growing. Its much harder than other algae ive seen and its only growing on the outer edges of my returns.
They look like hydroids to me. Rip some of it off and look at it under a magnifying glass, preferably in water. If there's a filterfeeder in it, it'll come out of the tip visibly.
+1 looks close to this type flow may be hiding the end in the pic on your penductors