Well, there certainly are a couple of things that needs some work. I believe once these problems are worked out, you will see some marked improvement.
At a temp of 86 degrees, the water your goldie is living in is very low in dissolved oxygen. This, in itself, can and usually will cause goldfish to become inactive. Usually they will pipe at the waters surface or sit on the bottom. Either way, I suggest upping the aeration by adding a bubble wall to his tank. Even though you have an aerator hooked up to a little filter, its o2 increasing ability is hindered because of the filter. Leave the filter and get another aerator with bubble wall.
Another thing that concerns me (well, your goldie) is the difference in pH (and KH) from the tap to the tank. KH is what keeps your pH stable. If the kH is low or drops, the pH will plunge as a result. This as well as low o2 levels, causes many symptoms to appear. I highly suspect that the pH diff is the main culprit here. Fixing the pH/KH problem might or might not cause an immediate improvement. It just depends on the extent of the damage done.
Good news though! His appetite is perhaps the best sign you can hope for. With him eating, it will make a recovery all that much easier.
Ok, how to fix your water chemistry problems remains to be seen. There are several ways (baking soda, crushed oyster shells, crushed coral, commercially bought buffers) to increase your KH to more optimal levels. Figuring out wich one will work best for you will be by trial and error. There really isn't any other way. Just whatever you do, do it in small increments so that any sudden changes to pH in the tank are minimal.
So, I suggest that you start a thread in the water chemistry forum for further guidance. There, you should recieve some very good advice on how to fix this. In the meantime, you are going to have to start doing a lot more waterchanges to keep your pH steady. Daily testing and waterchanges are going to become a chore until you get a good regemine figured out. Once done, your waterchanges can resume to once or twice a week again.
Go ahead and start by doing a 25% waterchange. let sit for an hour and then do another 25% waterchange. Etc. Etc. Test after each change until the pH in the tank is matching that of that tank. Remember, slowly but surely. Once the pH from the tank matches that of the tank, start teting the pH daily. Whenever you see a drop (however slight) in pH, do a large enough waterchange to keep it there. After you get the pH up and steady in the tank, you can begin working with whatever medium is chosen to control KH.
I'm going to go ahead and move this thread to the water chemistry forum for you. That way, all the info is right there.
Good luck!