i have a pictus catfish and 2 irredesant sharks in my 30 gallon tank. they all have ick. i have used malachite green & formalin for a week and a half with no charcol in my filter. it looked like it was gone so i put charcol back in my filtration and in 2 days it was back, my fish are not eating and i am getting worried. i am treating again but they look awful. i need some advise...