It's not the tank size so much as fish incompatibility. Goldifsh should be kept with only other goldfish as they're very messy, and neither loaches nor goldfish are compatible with angelfish. I also wouldn't keep so many large bottom dwellers together.
Yes I have 1 goldfish that will be leaving soon! The loaches and the angelfish will be separated as I do love the loaches but they are growing very fast and eat all the food before any other fish gets any!