My guppy's sick and the internet has no answers!

My guppy had been acting lethargic for a bit so I put him in a 2.5 gallon hospital tank where he's been separated for a couple weeks. Yesterday I found a raised bump on his side, maybe half a centimeter from the base of his tail. It doesn't appear to be filled with fluid, and it isn't discolored. I couldn't find any answers online, so I simply added a little extra aquarium salt to see if that would help. Today, though he is still eating and does not have clamped fins, he is even more lethargic, laying motionless on top of the heater and sometimes trembling. I've done one water change in case I accidentally put too much salt, and plan to do another. Unfortunately I don't know the water parameters since test kits are a bit expensive, but if it comes down to it I could buy one.

Any advice?

 

Pic please?

Also parameters would be good to know to rule out poor water quality. You can ask an LFS to test it for you.

We also need to know what tank he was kept in before, with what, for how long, temperature, diet, etc

 

Pic please?

Also parameters would be good to know to rule out poor water quality. You can ask an LFS to test it for you.

We also need to know what tank he was kept in before, with what, for how long, temperature, diet, etc

Thanks for your reply, and sorry for the wait, I didn't get a notification for it! I've attached some pictures, although they aren't great quality since he wouldn't stay still. I haven't been able to find a LFS nearby that tests water, but I will keep looking! Before, he was kept in a five gallon with two other male guppies, I've had them for four months, at 76 degrees, with a diet of Top Fin pellets and the occasional bloodworm treat.

 

just a small guess- benign tumor or bloated internal organ. I really cannot tell from the image though.
An internal bloated organ may be caused by stress or poor diet/care conditions. A benign tumor should not bother him at all. What worries me is his lethargy. You need to know your water parameters to rule out poor water quality as a cause for this. Is this 2.5 hospital tank filtered and cycled? If not, you'll only do him worse.

 

just a small guess- benign tumor or bloated internal organ. I really cannot tell from the image though.
An internal bloated organ may be caused by stress or poor diet/care conditions. A benign tumor should not bother him at all. What worries me is his lethargy. You need to know your water parameters to rule out poor water quality as a cause for this. Is this 2.5 hospital tank filtered and cycled? If not, you'll only do him worse.

Hey sorry for the late reply, I've finally been able to get out and get a test kit. So his parameters are pH 7.6; ammonia 0-.25 (can't really get much more specific); nitrite 0, nitrate 30ppm (it's in our water supply, so water changes don't help).
His potential tumor seems to have shrunk, but he's still occasionally shaking and having trouble swimming. He acts fairly normal during feeding and when I approach the tank, but any other time he's lying in the rocks. Is it possible that the tumor pushed on his swim bladder and is causing this? And theoretically wouldn't that have stopped as the tumor shrunk?

 

How white is the tumor ? It could be fungal disease or worse, columnaris disease

 

How white is the tumor ? It could be fungal disease or worse, columnaris disease

The tumor isn't white, it's the same color as the rest of his body. It's just a raised bump, not discolored. I've looked at the symptoms for columnaris and it doesn't appear to be the cause, and it doesn't look like fungus.