The tank size is good for a goldfish. QuickCure is hailed as being a great Ick medication, however there are differing opinions about the Maroxy. My advice is to do a 25% water change tonight, if you haven't already done so, and another in seven days.
Take him off the Maroxy, as over-medicating him will do more harm than good. Continue using Quick Cure, and add in some aquarium salt. The salt adds electrolytes that are beneficial to the fish, and also eases their stress. A 1/2 cup of salt should work fine.
I also recommend adding in some Stress Coat. I would add about 4-5 capfulls of Stress Coat into the tank, as it contains Aloe Vera and will help soothe the damage that the Ick has done on the skin of the fish.
Do this, and continue the Quick Cure, without the Maroxy, for 7 days. If you do not notice dramatic improvement within 7 days, quit the Quick Cure. After that, do another 25% water change on the tank and purchase a medicine called CopperSafe made by Mardel. It is another good Ick medication that has proven itself for having some good results in combating the disease.
Hope this helps!
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