one eyed fish with possible fin rot?

Question
I was in the local wal-mart and stopped to see the fish. I noticed a black moor in the goldfish tank that only had one eye. He looked rather weak. I'm not sure if it was from poor conditions, or just a sick little guy, or both. The other goldfish seemed fairly active but I decided to try and save this one and get him out. I bought him. It was about a five minute drive to my house and I was certain he wasn't going to make it. He was barely moving and started to float to the side and just flutter his gils near the surface. During the whole acclimation process I decided to try and give him some food. (I'm not sure why, I know you shouldn't but something told me to) He ate vigorously!!! He is one eyed so it took him a while to find it, but once he did he ate every bit! And quickly! I think he might have been starved from the healthier fish eating all the food before he could even find it. Anyway, he looks like he might be fine now but his fins are looking a little bent up and kind of frayed at the ends. He seems to be swimming pretty actively (top, middle, and bottom) but how do i tell if it's fin rot or from being picked on by other fish? Out of all the fish tanks I've had ick was my worst problem. I have him in a tank by himself now but didn't know if I should add a tank mate for him or not. I'm just looking for some advice to get this poor little one eyed fish happy again. Any advice?

Answer
I forgot to mention that in order for him to have a friend the tank would have to be big enough for both. Each goldfish needs 10 gallons because they get so big and messy. If the tank he is in now is newly set up it still has to go through the break-in period too. You will want to wait to add a friend until that is over. Here is my web page about new tank syndrome to help you with it;

http://www.xanga.com/Expert_Fish_Help

At Your Service;
Chris Robbins