I am MUCH encouraged to think that I have finally found the cause of my water quality problems. As soon as I got home tonight I did a 40% water change and sucked up as much of the rotting food out of the tank as I could. I would like to skip feeding them today. I hope that is okay. What do you all say to skipping a day of food now and then? In about an hour I will do testing to see what I get.There's your problem.... you have been overfeeding 90%. Don't believe everything you hear or read. Plenty of shops and books still tell you you can keep goldfish (plural) in a bowl or 10 G tank. The "stomach" of a small fish is about the size of it's eye.
Just ask on the forum... there are many here who have been doing it for decades.