Cause related to DOC may be hard to prove without controlled experiments & proper equipment. What I have is anecdotal data which may not be able to demonstrate root cause or nail down to the factors affecting the result. Bacteria is a new topic & am keen to explore more.
I did notice 2 incidences of massive SPS RTN (really overnight) several days apart. A slimy cloud was observed just above the rocks. Sections of various SPS colonies in contact with the slimy cloud had the flesh peel off overnight. Everything else above it was OK. In both incidences, the tank were fed with Ocean Nutrition Oyster Feast the night before. Don't get me wrong.... Oyster Feast is fantastic food for the tank. But this bottle went bad -> And hence I was actually dosing massive ammonia laden liquid onto the corals.
Once the cloud was turkey basted away, the RTN stopped. Coral did not recede further.
I mention this here to highlight the importance of ensuring you feed the freshest food possible. I noticed something odd on this bottle of Oyster Feast. Whenever the cap was popped open, there was air gushing out (like opening a coke bottle). I didn't recall this in previous bottles used. I supposed that it'll stink of fishy stuff if it had gone bad. But instead it smelt a little sour. I thought it was odd but continued to use it because good money was spent of it. (just a week old...$30 bottle of food). After 2 incidences, I put some oyster feast under the microscope. 2 observations :
1) Bubbles continued to form between the 2 layers of glass slide. Some kind of gas (CO2? Nitrogen?). The drop of oyster feast is fermenting.
2) The liquid was quite clear. Very tiny bits were present but most of it was liquid. It is very different from microscopy pic of what it should look like.
My conclusion is that the food had gone bad. The addition of this increased the level of ammonia / DOC, arising in a cloud of ciliates. Some reefers may refer this as 'bacteria cloud' which in reality is a bacteria layer loaded with ciliates.