I believe it passed several pages ago.Warm water contains a lot less dissolved oxygen. Both fish and bacteria require dissolved oxygen for their life processes.
I can't speak to the corals/invertebrates in your tank, but lowering that slowly is way too long for fish. Get it down to around 81 right away, and then move more slowly down to 78. I tell people that this is akin to being outdoors in the winter with no coat. Which would you rather do, move into the house or first spend 6 hours in an unheated garage?
Temperature shock for fish really isn't a thing - except for temperate water species exposed to a change greater than 8 degrees. Corals, adapted to higher temperatures are a different matter, as are shrimp.
With 8 pages on this thread, I may have missed this, but what is the eels respiration rate? If the high temperature is the root cause, then the eel's respiration rate will be elevated - >100 to 120 BPM.
I've kept snowflakes at 82 degrees with no issues, remember, these are inshore fish and the shallow reefs get really warm there.
Jay