Swimming Decorator crab

OK I have a theory and only a theory. As long as I have been keeping fish I am drawn to odd shaped fish like copperbands and long nose butterflies but I could never keep them as long as most other fish and looking back there were two causes for their deaths. One was jumping out. For some reason those types of fish like to jump. I lost about half of them from that. The rest of them died from something else. Last year I lost a copperband that got a bump and then a sore on it's side just before dying. I remembered that a lot of them got that before dying and I atributed it to bad collection practices. I figured skinny fish were more subject to tramatic injury because they are so skinny. The autopsy of that last copperband showed internal bleeding at the site of the lump and tissue necropsy or dead tissue.
A few days ago I noticed a lump start to form on my new long nose butterly and I knew the fish would die like the others so I caught her and put her in a small tank with some antibiotic which I knew would not help the fish but I figured it would help the water from becomming too fouled when the fish died.
This morning the fish was dead as I know it would be but unfortunately a fish starts to deteriorate rather fast when it is dead. I did however have enough time to do an autopsy on this long nose butterfly.
It too had the same diagnosis as the others and after doing some research I came to a conclusion as to the causes of the deaths of these skinny fish.
Small fish of this type are very thin, the tissue over their bones, especially towards the back where these lesions start is practically non existant and is really just skin with almost no tissue.
This is where the lesions start on most of these fish.
My theory is that these fish, especially when young, when they are kept in a tank are suseptable to
"Methemoglobinemia".
This is not as complicated as it sounds. What happens is that when fish injest nitrate laden water such as in many tanks, the anerobic bacteria in their gut converts the nitrate to nitrite, just as it would do in our substrait.
The blood converts a small amount of nitrite into Methemoglobin. Methemoglobin in small amounts is not enough to kill the fish but it causes the blood to lose some of it's capacity to carry oxygen.
In most fish there would be symptoms like rapid breathing or breathing from the surface. In more severe cases sores form on the head or lateral line from lack of oxygen to those areas and subsequent tissue death, but "I" feel especially in skinny fish it manifests itself in the thin parts of the animal where blood flow would be minimal such as the rear end of those types of fish. Methemoglobitis is not that common in fish from the sea because the nitrate is much lower in the sea.
This disease is also called "Brown blood disease" and it is easy to spot in an autopsy as was the case in these last two fish.
Now I am not a doctor, researcher, neurologist, entomologist, parasycologist or any other type of ist. I am an electrician with a fish tank. These are just my observations and my theories. I have noticed these lumps forming on most of the longnose and copperbands I have ever lost and I lost plenty of them, probably dozens.
Metheline blue would reverse the effects of methemoglobitis if the fish could be caught but if it is put back in the same tank, itwould probably get it again.
I will continue to research this but I would like to know if any one else has lost these types of fish and if you noticed a lump or sore on the skinny parts of the fish
You can see it start to form in the slightly dark spot near the bottom center of this copperband


And you can easily see it on this yellow wrasse who also died and the autopsy was the same.