And, to add insult to injury, historically I have had a huge battle with NO3, some PO4. Haven't even bothered testing in forever, until right now. Both PO4 and NO3 at 0ppm. FML
Just did water change, going to hit it with the Kent Mg OD, see what that does. Some of the algae elsewhere is bryopsis for sure, and this stuff looks similar.
Recent sea hare addition didn't touch it, and has apparently died. Or is hiding REALLY well
