The food is obviously the source of the odor.Within about an hour of feeding, and lasting for about 12-14 hours after, this tank smells and it fills my entire house with an overwhelming earthy/bitter smell.
Different tank size, different fish, different dead spots, different filtration, etc-etc can all be part of the problem, or solution to the problem, but the food itself is clearly the source of the odor.
Don't feed for a week, and you will be odor free the entire time. lol