Hi Jo,
Honestly, I am not sure whether we can totally eradicate ich from our tank for its still unkown where ich comes from in the first place. Some experts claims that ich is a condition not available in the wild but in captivity.
Personally, there was a time where I struggled with ich, I have also tried many suggestions listed here. I find that ich no matter how will visit our fishes when the parameters are out or there is a new addition. Thus, my personal belief is that, "Ich is stress induced - if we remove stress and maintain a stable parameters, our fishes will be able to overcome ich".
HTH