Species Spacific Info
Comets need about 50 gallons EACH. Just for 3 comets, you'd be looking at a 150 gallon tank... realistically put, a smaller pond.
Fancy Goldfish need about 20 gallons for the first fish, then 10-15 gallons per additional fish. So for your three fancies, you'd be looking at a 55 gallon tank... hey, that’s what you have now!
Loaches require a group many times... but it depends on the species. Some species get very large too. You should know what you have, it would help us greatly!
Sizes
Comets get about 12-16 inches. Close to two feet long isn't uncommon in fully-grown comets.
Fancy Goldfish get 10-12 inches usually and are very round-ish in shape. This makes it hard for them to turn around in smaller setups.
loaches, as I said it depends on which kind of loach you have. Some get 4-5 inches, others get over a foot long!
Do you see why your setup is not adequate for all these fish? Sure, it "looks" like it could work now, but these fish are nowhere near fully-grown yet.