Yes, but I bet your crabs and urchin hate you.
We can cure ich just like we can keep ourselves relatively safe from bacteria diseases if we stay on antibiotics for the rest of our life. Of course that would cause all sorts of other problems.
When the hobby started we used to keep copper in our tanks continuously, and we had no ich. Our fish were never real healthy because the copper gave them other things. Eventually human doctors learned to allow us to use our own immune system to protect us from most diseases and eventually most people in this hobby will learn how to use the fishes immune system to protect them from ich. Many older hobbiests already learned about this.
Good luck and I hope your urchin starts talking to you.