You say you got a used tank that came with fish
How did you transport everything? Did you drain ALL the water out and put the fish in separate containers?
-If yes then you may have a cycle problem
The bubbles are from you filling a large sum of water up quickly which causes some sort of checmical reaction and makes some sort of dissolved-gas get trapped in your tank (Normally this is experienced during cycle but if your having cycle problems im not sure how this will play out for your fish)
I know everybody on here likes to scream this, and its really like beating a dead horse but. It is very likely that your fish's spots are caused by the water quality. Id say you could fix this by changing some water BUT if were on the cycle problem im not sure how to fix this.
Id get some test strips just to double check on the water quality as many members will drill this into your head.
Well hoping to hear from you :)
If you have ich im confused at how your fish got it as you say the tank was used? And came with fish? How old were the fish when you bought it? Ich CANNOT just "appear" it must be brought in from the petstores sickly fish. It will also look like you took a wet fish out the water and took a hand full of salt and threw it at the fish (buncha white dots)
There are great stickys on this forum about how to battle ich