Pleco With Abscess?!

Hi all,
A few months ago I posted with an emergency that my pleco had badly burnt itself on the heater. Well this healed up and has been fine ever since. I noticed yesterday during my weekly water change that he had a lump on his side. So I netted him picked him up and had a look, it seems that he has some kind of abscess under his skin, it has got bigger today and I dont know what to do. The skin is very soft compared to his armoured part, and the lump is really soft like a balloon instead of hard as I expected it to be.
What could this be?
I had a neon tetra die yesterday of suspected dropsy so could this be the problem?
The pleco is around 6 inches and in a 40 gallon tank.

pH: 6
Ammonia : 0
Nitrate: 0
Nitrite : 0

I can try to get pictures if needed, Thanks.

Probably a simple explanation but why is the Nitrate 0? Surely there should be some Nitrate Not shaking the bottle hard enough?

I'll go test again ;-) at first I thought it was probably digestive problems but it is on his side, not his tummy.

Ok so it seems that I did the test completely wrong last time **note to self- READ THE INSTRUCTIONS***

Turns out the nitrate is actually 80ppm, could this be the problem?

I only did a water change yesterday so surely it should be lower than that, there are no plants in there though, just algae that my pleco is supposed to eat ;-)

What type of plec is it?
As far as I am aware, most plecs are good for algae eating when they are small as this is part of their diet, but as they grow, it just isn't substantial enough and most turn their noses up to it.
 
I don't see how Nitrate could have an immediate effect on the abscess, even at 80ppm I wouldn't say it's especially dangerous but there is great controversy here - it's certainly not as toxic as Ammonia and Nitrite.
How much of a water change did you do yesterday? If for example it was only 20%, your Nitrate would've been around 100ppm, as you've only technically taken out 20% of it. The high Nitrate levels would also be quite a good explanation as to why you have algae in there in the first place!
 
How often do you do water changes?
While you reply to this, I'm going to have a look about abscesses. Could you post a picture? 

Firstly, plecos come in all varieties in terms of diet. Some are carnivores, some omnivores, some aufwuks feeders and some vegetarian. One of the features which facilitates the identification of plecos is their dentition which is adapted to the different feeding preferences.
 
At a guess, could what you are seeing be a heater burn?  There are other, less likely, possibilities as well.
 
I find it often useless to use a nitrate kits on fw tanks as the results are so unreliable and because regular weekly water changes should keep nitrate under control.

TwoTankAmin said:

Firstly, plecos come in all varieties in terms of diet. Some are carnivores, some omnivores, some aufwuks feeders and some vegetarian. One of the features which facilitates the identification of plecos is their dentition which is adapted to the different feeding preferences.
 
At a guess, could what you are seeing be a heater burn?  There are other, less likely, possibilities as well.
 
I find it often useless to use a nitrate kits on fw tanks as the results are so unreliable and because regular weekly water changes should keep nitrate under control.

Click to expand...

 
Yeah, the plec man is here to save the day

It is a common pleco, I did around a 20% change yesterday, and a 50% the day before because my pH is abit low so I tried to bring it up again. I'll try to get some pics but I'll have to take it out of his cave so could take a while, I dont want to hurt him :'(

Ok so here are the pics, they are the worst pics in the world but you can see where the lump is from the light shining in it. His tummy feels raised too with something like a gas pocket in there which stretches around to where his burn was. It isn't another burn tho.
And thanks for replies so far ;-)

Hate to say it, but I am stumped. Parasites? Worms? Infection? It looks fatter than it should I think.
 
Without have any sort of handle on things, anything I might suggest would be a guess. The best thing I can suggest is to try posting on http/www.planetcatfish.com/index.php for help.