no, ich is not in every tank. Ich is in every tank that do not go to the process of quarantine yes.
I don't have any ich in my main tank but I do a strict quarantine on eveything. Ich is a parasite, and it does not come out of thin air. It does not have to be there at all.
Healthy fish still have it wether you see it or not, and still suffer from it wether you see it or not. At the fist sign if weakness it will be an outbreak and fish death. It is best to quarantine and dip all new fish.
Look at the quarantine process of the
www.liveaquaria.com Diver's den:
I don't go to that extend but I guess a formaline dip should be the first step on all fish.
http://www.liveaquaria.com/general/g...al_pagesid=425
I dip my fish in Seachem Paraguard for 1 hour if they can stand it, but at least 30 minutes. Then I treat with Praziquantal for a week and that is a reef safe med that take care of flukes and internal parasites.
I had ich in my quarantine on a blue hippo tang and a kole tang and treated both well with hyposalinity.
In that time I was not doing the dip but now I do it and often that's enough to kill everything right from the start. I also have real formaline 37% but I find Paraguard safer.