Increase water temperature
The ick parasite transitions through three life cycles. One involves the attachment to the goldfish in the adult phase. The second happens when the ick drops off the fish to the bottom of the aquarium to enter the cyst cycle. The final phase involves the newly hatched icks that free-swim in the aquarium looking for a host fish. The only time to treat the icks is during this free-swimming phase. By raising the water temperature, the life cycle of the ick speeds up and shortens, thus there is less time to attach to the goldfish. Make sure when raising the temperature not to exceed a safe environment for the goldfish.
Aerate Water
Another natural treatment involves adding oxygen, or aerating, the water in the goldfish's aquarium. This treatment works with elevated temperatures as warm water contains less oxygen so the intent is to maintain or increase levels.
Water Changes
Besides raising the temperature and aerating water, replacement of the water frequently assists in the treatment of ick. Fresh clean water combats the ick and removes any free-swimming parasites as well. Making a habit of daily water changes should produce results. Cleaning the gravel and anything else in the aquarium while changing the water also provides another treatment.
More Space
One reason icks have success in aquariums is the small area. A parasite has to find a host, and the smaller the area the easier that becomes. So, if possible, spread out the goldfish to more than one aquarium or limit the number of goldfish. Either way, the icks have fewer choices and less likelihood of infestation.