Not a problem.
Don't feed goldfish. He doesn't need them, and you risk transferring parasites from the filthy pet store feeder tank to your beautiful catfish. In addition, they can cause other health problems, as well. Here's a link to some info on Thiaminase:
http://www.monsterfishkeepers.com/forums/showthread.php?t=167891&highlight=feeders+thiaminase
Try some variety in the food. Fish filets, squid, Massivore, Aqua Stable, Algae Wafers, etc... You want to make sure he's getting everything he needs, and one food source isn't going to do that for him. Also, he can have the shell and tail -- they're full of calcium and other good stuff -- YUM.
If these are your current water parameters, I see no problem with them, and I don't think this is the problem.
If there is no heater in the tank, then there is no way it is a constant 75 degrees. So, the reason for a heater here, is to heat the water to an optimal temp, say, 76 or 78, and keep it there. You set the heater, and it only runs in order to keep the tank up to that temp... it shuts itself off.
You can add epsom salt to help with bloat and possible constipation. I have to admit, I'm a little lazy so I'm going to copy and past some of my past posts with this info, and provide a link to a recent thread that these are coming from, so you can see them in context:
You should add the Epsom in increments. Treat 1/2 of the tank today, and the other 1/2 tomorrow... so if it were ten gallons (I know it's not haha) you'd do a half a tablespoon today, and half tomorrow. Take out some tank water and mix it up in a little bucket or pitcher before you put it in the tank, just like you would with regular salt. If you have trouble getting it to melt, use hot water and add a little Prime or whatever you use, and then just let it sit and get to room temp..
Here's the thread I copied from:
http://www.monsterfishkeepers.com/forums/showthread.php?t=283787&page=2
If you don't see a change in this guy within three days of adding the last dose of Epsom salt, then it's not going to work, and we have to figure out what else could be going wrong (i.e., a parasite of some sort).
How does his poo look?