Awww :3 Thanks aokashi!
If they look like they are hiding from the current, they probably are. Goldfish should be all over the tank trying to eat everything. But you are right in thinking they need a lot of filtration. I have heavy filters on my goldfish tank, but I have to baffle them because the current is too strong. Depending on the make of the filter, a water bottle baffle might work. Or something as simple as an aquarium sponge in front of the outflow.
But that brings me to my next point (which you may already be aware of). The comets will outgrow a 20 gal tank. It was wonderful of you to upgrade them, but they will still need more. Honestly they do best in ponds as they would need a 125+ gal tank to satisfy their swimming and space needs. So. Have you ever thought about putting in a pond?