Goldies do need decent aeration in the tank. They can breath air from the top, but prolonged exposure to this can produce swim bladder disease, especially in the fancy variety. With your other fish doing this, it could be poor aeration. This can be caused by the increase of ammonia and/or nitrite. It could also be that your filter/airpump (aerator) cannot keep up with the bio load and fish needs. What do you have along the lines of
O2?
Goldfish also are not recommended to be placed in a plain bowl. They are one of the dirtiest fish around and will need good filtration.
UGF's typically do not work because they are a member of the carp family and like to rumage through the gravel.
The recommended temperature ranges anywhere from 56F to 72F, though they can sustain tropical conditions,(Mine is at 80F right now, uncontrollably), but, as mentioned, you should NOT keep them with tropicals. A lot also depends on the variety of goldfish: e.g Comets, fancy, feeders.
Also, the 1" of fish per gallon should NOT apply to goldfish. They really need a good surface area and suggestions range anywhere from 10 gallons to 20 gallons for the first fish (regardless of size) and 10 gallons for every fish after that (this is a good reason why a "bowl" will not work). For your 55 gallon tank, using the smaller suggested stocking rule, you're already down to 35" of fish left for your tropicals. Add in the recommended 10 gallons per Angel, and you're up to 60 gallons with just those 6 fish. I would also suggest that you are probably a bit overstocked. For this reason alone, you need to do something with the goldfish at the very least.
