I’m battling same thing. I have a thread about it. Moved my fish to a quarantine tank to treat. The life cycle of ich can last 30 days. It’s still there even if looks like it’s gone. Cleaner shrimp don’t help. Have to focus on nutrient and quarantine tank to treat. Read the link on the ich life cycle, it’s very informative and helped me a lot. Unfortunately the only way to really prevent ich is a QT tank before you introduce into display tank. Your 100g now has ich as well. It stinks!! Again I’m going through same thing right now Good luck and keep posting.