My 2 montipora’s green and red starting to bleach out of nowhere. From top or some edges in. All soft corals doing great. I ceased water changes for 2 months to raise no3 and no4 to detectable as I’ve always had to clean of water and was battling a cyno outbreak. Tank 2 years old. Been reefing 10+ years and am just no starting to dos po3 and po4. Currently no3 is 1.5 and no4 13ppb. Lighting hasn’t changed . Any input would be appreciated . No nudibrnches seen.