One fish has ich with the others get it?

first off a blue tang shouldnt be in less than a 90 gallon tank, also if you had problems with ich previously the last thing you should have done is add the tang. blue tangs always have ich, just sometimes its more pronounced and things an make it more pronounced such as stress and at night it becomes pronounce as well. theres not really a way to ever get rid of it once you think its gone the littlest thing can trigger it to come back with more force than before.

 

Ok we have had this discussion on the 90 vs the 75 it is 4 inches shallower which makes almost no difference the fish would never even notice the 4 inch difference. and also it will not always have ich it can recover from it and not have ich anymore but can still be affected by it if it is introduced to it again.