in my personal opinion, ich is ever present in the a marine tank setup.it's a matter of how strong your fish is able to fight it off. You can try Hypo but if you have many corals in your tank which have already encrusted to your rocks then it is impossible to remove. So your next alternative is to catch the fish and QT them again using the Hypo method and leave your tank fishless for about 6 weeks.
I did that when I first started out and I had 2 outbreaks of velvet... all my fish died accept for my tomato clown which managed to survive 2 outbreaks AND freshwater dipping.
If you are unable to catch your fish, then it's a matter of hoping they carry on eating and build up strength. I tend to overfeed whenever I add in new fishes, more pellets, more flakes, I use Dr Basselers and I soak my PE Mysis in Selcon & Garlic Guard for my fishes to eat. As long as the fish is still eating and swimming, then it's alright.
when you add new fish to your system, it's good to float the bag so that the temp of the water in the bag gradually becomes the same as your tank or for sensitive fishes like Powders and tangs, to use the drip method.
good luck