Reason I asked is i am having a couple of my well established pieces(2+ years ORA tri color validia and ORA Miami orchid ) showing STN with no pests in tank. I have dipped them several times and know the signs to look for with no success in stopping said event.

Parameters are
salinity 1.025
alk 9
cal 450
mg 1400
nitrates 5-10(a tad high but doing a water change presently)

Thanks