help!!!!!!losing my pleco at rapid rate!!!

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Just returned from vacation .Woke up this morning to find my pleco belly up on gravel.He rolled over but definetly looks like a problem.I noticed he didnt eat any of his food last night.He was ok when I left four days ago .This fish is my oldest fish in the house almost 6years .He has always been healthy .Now I have this out of nowhere.He has been thrashing around tank like hes in pain and is now laying upside down breathing rapidly.There is no outside obvious indications of disease or trauma.I have no idea where to even begin with this.Im a pretty experienced fish keeper but clue less as to what Im dealing with.All parameters in tank are normal.6.8 ph ,0 ammonia ,0nitrite,20 ppm nitrate,kh 70ppm,gh 70ppm,temp 82 f.Any help would be greatly appreciated.

[Holly9937]

Is it possible that anything happened when you were gone? Could any chemicals or something weird gotten into the tank? What about the temp, has that been constant while you were gone?

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Not likely.We did have someone looking after our other animals,but our person is very reliable as far as following instructions.The instructions I leave have always been dont feed my fish!!!!! The tank got a waterchange before I left town ,and fish was fed and eating well.Im guessing a possible bacterial infection because I would think parasites would have turned up in the six years Ive had this fish.This is sad...I am quit fond of this guy.Im dragging out the quarintine tank at this point I guess.

[Balloonhead]

I have a sick pleco too.... though not as sick as yours. I have him on fish anti-biotics and it looks like he's gonna make it.