Need help figuring out what's wrong with my fish

Hello everyone, I have recently come into some recent troubles with my goldfish. This one goldfish in particular started exhibiting these symptoms: it has two white streaks on its body and one of its eyes(the right one) have become really red.

I have a 14 gallon tank and recently, the ammonium levels in my tank are a little bit above average (around .25), because I overfed him. I took him to my local aquarium and they told me to do was change the water and things would be fine. I started feeding him less and did several water changes, but he showed no signs of improvement.

Here are some pictures that I recently took of him:

http://img203.imageshack.us/img203/4097/dscn1471j.jpg
http://img15.imageshack.us/img15/9489/dscn1476f.jpg
http://img191.imageshack.us/img191/4403/dscn1478p.jpg
http://img713.imageshack.us/img713/7442/dscn14761.jpg

The odd thing is that the other goldfish I have is fine. I also have 5 minnows in the tanks as well. Recently one of the minnows died and its throat looked like it had a bunch of cuts on it...

Any help in figuring out what's wrong with him would be greatly appreciated! I have been worrying about the poor fella for the past week... Thanks in advance

-goldfishluver