Discus swimming erraticaly then Dieing

[dntx5b9]

I lost two discus to this about three weeks ago. Very interesting how this doesn't seem too uncommon in discus. I have never seen this happen to other fish. My fish were breathing heavy at the time, and I added an airstone since then. Things have gotten a lot better since I added the airstoe.

[MoanaVic]

It has been happening for about 2 weeks now in one of our 2 tanks

first the fish just swims in circles or goes crazy smashing into everything and the glass, all of the fish a respiring quite quickly despite having the sponge filter on max airflow(there is also a canister filter running)
the discus are all about the 8cm mark and we've had them for about 3months now and the tanks were set up new for them

then they die a day or 2 later
it only happens with one fish at a time (in a tank with 10 fish in it), all of the rest are fine and show no signs of any problems, then after one dies another starts showing signs a few days later
they are all similar size, the pH is around 6.5, ammonia 0ppm, nitrite 0ppm, and low nitrate around 5-10ppm, temp 28C

water changes are about 30% 2-3 times a week
they're still eating and the only other fish we had in the tank was guppies but we removed them about a week ago

any help would be golden in solving this mystery illness
thanks

I realize this all happened a long time ago, but I’m having this same sequence happening in my discus tank. What was the final outcome in your tank and did you ever figure out why?

In my 90-gallon tank with 5 fish, one starts hiding then acting erratically and dies a day or two later, then the second discus does the same a day later. Now the third fish is starting to behave the same a day after the second died. Tank has been up for 4 years though 2 fish were added 2 months ago after 1 month QT. Water parameters have been stable, temp 85F, ammonia 0, nitrite 0, nitrate less than 10, pH 7.4, KH 3, GH 5.

Frustrating to say the least.