here is what you gotta do. same thing happened to me. i was able to save my last two torches, i lost the rest.
Its process of elimination.
Once you ruled out too much flow or light. Then you rule out water quality. lots of testing. if its determined that none of those are the issue. Then there are the two that have affected me in the past.
1.) Bacterial infection, the most likely culprit. Keep in mind there is more than BJD for infections. you wont always see the brown jelly and it could still have an infection. if this is thought to be the cause, you have to options
a.) full tank treatment. i dosed my tank in cipro, and installed a UV sterilizer. this fixed the problem for me.
b.) Out of tank treatment. KFC dip. either method will work. i prefer whole tank if you really think the problem is an infection. if your not sure if you have an infection, out of tank is the better option.
2.) Pests. months later (actually recently, just past few weeks) my torches started to look recessed and flat. i did a dip in revive, iodine, and hydrogen peroxide, one at a time. what happened next i would have never guessed. tons of tiny 5mm long bristleworms fell out of the inside of the torches. they literally buried themselves inside one of my torches, and on the other two were crawling all along the sides. my best guess is my target feeding was somehow drawing them in. i dont know. but they were bothering the hell out of torches. there is also flatworms and spiderbugs that can bother them.
for both these causes dips will help. but again, these two culprits must be the last options in the list of process of elimination. as 9/10 times flow or water quality is the problem. good luck!