Hello Fish...
An organic minced garlic is fine for anything you keep in a tank. Choose one of the brands with no additives. Just water and the garlic. Very nutritional. My fish really go for it. Ich is a tricky parasite. It can live on the skin of fish for some time with no risk to a healthy fish. However, a couple of missed water changes or a sudden change in the water chemistry can stress even a healthy fish and affect its immune system, leaving it open to infection.
The best thing you can do is change most of the tank water weekly, feed just a little of a variety of flakes, freeze dried and even frozen foods and add some stems of a floating plant to the tank to keep the water cleaner between water changes.
B