It also doesnt mean it came in on the tang, the tangs could have just exacerbated the problem. They tend to be magnets for ich. If you aren't going to remove them, you must feed as often as possible and feed high quality frozen foods and nori. As someone else said, do not raise the temp. that will only make it harder for them to breath and add stress. There are other mechanisms to aid in helping them manage it such as diatom filters, ozone generators, and UV sterilization. Again as someone else stated it sounds more like velvet so you may not have time on your side to implement those definitely worth looking into going forward. What are you currently feeding them and how often?