leaning discus

[Agent]

Think I need some help again please. One of my discus has started to lean on an angle (in the comunity tank), he has aslo gone brown in colour & is twitching, when I left for work this morning, he was fine, all this shappened in 8 hours!. Did a water change on Saturday 30-40%, on Sunday did all the tests & everythinhg was fine, checked Amonia & Nitrite levels tonight & all was really good. The only thing out of the ordinary was, I noticed a small amount of black slightly fury fungus starting to grow at the top of the large tree root that is the centre feature of the tank, dont think this is the problem but thought I had better mention it in case it means anything.
Any suggestions???
Thanks,
Rob....

[Agent]

It now looks like the problem Discus is back to normal colour & eating well, I did notice a scratch on him, this may have alarmed him a bit. When I saw the brown colour, I freaked, as I lost on a couple of weeks ago (he was sick when I got him)
Regards,
Rob...