Adult discus died after water change

[giorid]

Hi everyone, more bad news, sorry to say, it seems that discus and me aren't meant to be, unbelievable, but I managed to lose another big beautiful fish, have other discus in the same tank and they're doing fine, this particular discus developed a largish white area around one side of his head, like a discolouration of some sort, and died overnight, it happened a day after I did a 80% water change the white spot developed so fast I though it might have been ph burn but the other fish didn't show any effects. I had this particular fish from when he was small and now it was about 2 years old. The other discus are normal and doing fine, the water change was done with very clean conditioned water with the same temp. and ph. and did the checks for ammonia nitrite and nitrate, all negative, as I usually do it without any problems, I added some salt in case it might be a bacterial problem at the rate of 200gm/100L and fish look happy. I keep my tank very clean and it's a bare bottom tank, my question is, as anyone seen this happen before and know what could kill a fish so fast, read several discus books but couldn't find anything and nothing online, any imput appreciated, thanks.

[Mr Wild]

From the sounds of that it appears the fish was sick before the wc therfore I doubt it was the change that did it as you say you checked all the parameters first and if the death was from osmotic shock I would expect most if not all would be showing bad signs.

[Exotic Aquatic]

I have seen something not dissimilar happen when walking past a tank when the lights where off... i heard a bang! my shadow had triggered its startle/scatter reflex which is a natural defense from nocturnal predators. In any case the fish seemed fine. The next day i noticed a pale bruise on its head, 2 hours later it was on its side... 12 hours after that, dead.... and the "bruise" was larger still.

Since retelling this story i have heard of it happening to many other friends too! Unfortunately for me the fish i lost was a sub adult altum angel.

If your other fish are ok, dont give up for their sake, and for yours... Its a WONDERFUL hobby, and the highs WELL out weigh the lows you may suffer along the way.

Wishing you well, and happiness in your hobby,

Regards,
Adrian.