DO you have any softies in your tank?
Mushrooms, leather, palys. or rocordia?
I have a close friend that's been doing some research.
Softie corals have some of the most toxic poison of any living creature.
He's hypothesis on RTN is that the same toxin that comes from softies and leathers, might be the culprit.
I'm obviously not saying that that's what caused it, but it's kind of exciting to know people are researching RTN.
And it may sound like snake oil, but I've used ReefGrow's RTN destroyer and had awesome results.
Might be just coincidence, but i saved about half of my acros from RTN..
Food for thought