Hi, I have recently started to get problems with millepora and tenius (5 different colonies), they're polyps started turning brown, the coral itself did not change and is still the same base color with good growth and polyp extension, but the increased PE completely covers the coral in brown polyps, was pink and green previously, all other acropora have not changed and stayed the same color, tank is 18months old 450gallon sps dominated, no3: 10, po4: 0.08, alk: 8.6, cal: 430, mag: 1400. Par: 480(seneye), lights is a 8x80w Ati surounded by 8 AI Hydra 32's. 60 gallon Waterchange done every week. Anyone experienced something like this before or is there a obvious problem that is causing the brown polyps.