I agree with the garlic added to their food, I started making my own fish food..
here goes if anyone is interested;
~ frozen Pacific shrimp, I put it through a food processor. rough chop for the bigger fish (30 count bag, peeled)
~ Mysis shrimp
~ brine shrimp
and 3 gloves of garlic.. my fish love it and I have not had any other issues with ich
I also add about 1 cup of vitamin enriched flakes..
It can be a bit of a pain to make, takes me about an hour and the yield is enough for a month
p.s. don't tell anyone but I tend to be a heavier feeder..
brittle star fish and the corals love it too.
I also believe to that sometimes the equipment/utensils that we use could cause cross contamination especially if they are used for other kitchen chores..
just my 2cents..