Hello, I've kept a single loach in my community tank, which consists of livebearers and cory cats at most. Actually I kept 3 clown loach before, but 2 of them died months ago. One died in juvenile stage (as I had bought it when it was juvenile) and the other died in the odd way. The way it died, as I still remember, is quite intriguing. I saw its body, it was so thin that I can't feel the flesh in its body, as if the flesh was extracted and peeled out of the skin, and only the bones left under the skin. It looked like my dead clown loach was made of bones and skin only.

Few days ago, I removed chinese algae eater from my tank, for I've seen many mysterious deaths and torn fins everywhere until the day I found the fact that they are not the good choice for my community tank. But after that I saw my loach have the tail fins torn apart so severely that I thought it will gets fin rot and kills this loach in the matter of days. I'm quite sure that it must be caused the aggression made by the algae eater. Not wanting to give up, I added acrivlafine in my tank and now its fin looks much better than before. But then, the same things looked like happening once more. This last surviving loach in my tank is still active and full of appetite, actually. But I see the back of my loach is so thin, compared to the rest of its lower body part. I can almost see the upper body in its back gets thinner than it's supposed to be, as if the flesh on its back has been shrinking and only the bones under the skin is visible now. It's clearly like this last standing loach has the same symptoms as that of my previous one before.

My question is:
1. What's the disease of this loach?
2. What's causing this disease to occur?
3. What medication / action should I take?

Thanks in advance..