The tank is too small first of all. Goldfish, even FEEDERS get 8-12 inches at adulthood. Your goldfish would NOT like that much of a current in the tank, and would be VERY unhappy. Ich is killed at 82 degrees farenheit, however goldfish are a temperate water fish, they do not like it over 75 degrees at max. The heater setting is fine... just I would say the fish needs absolute minimum of 30g by the time it is bigger. If it is small it could be kept in a 10g for a LITTLE bit.. like.. 4 or 5 months is my longest suggestion.
Good luck.
