This!, they tend to do this when theyre upset.
A) Brushing against another Torch that is 'unfriendly', basically shooting him with toxins. Theyll either tend to die or get used to it with discomfort. I tend to get a 30% survivability rate if I leave them side by side. Thus now the moment I see this happen and its a new torch, its off to a new plot of land.
B) Could be an irritant in the water column itself. Have had issues with heavy metals before and ICP confirmed it and they would randomly start displaying this behavior. Solution - Ran poly filter through the outflow to remove whatever is in the water. Now run some polymer based gel beads that have helped significantly and dont require constant change. Torches have been doing good, moved 11 Torches and 15 hammers or so last night to a new tank and didnt change the water in the previous housed 20 gallon they were in for 1.5 months and the new tank they are huge today morning.
C) The worst of the worst, they have started getting a 'flu', some bacterial infection has started. You have to keep a close eye on this because I have had times before where I saw them 'flashing' like this and when I got home from work at night, corners of the flesh have started showing the satanic Brown Jelly Disease. Solution - Keep tabs of CIPROFLAXIN(yes please those that are against it dont bash me, but it has really saved my tank and I will stand by it), Once A & B have been indefinitely eliminated as the cause. START THE ANTIBIOTIC DOSE because now you are waging war with something that will slowly demolish all in your tank - Coral Wise. *Detailed information of CIPRO dosing can be found in this forum