If it has Ich then they're present in your entire tank. Heres a quick rundown on Ich:
1. The trophont stage will spend three to seven days attached to the fish. After that.. 2. The trophont leaves the fish and turns to the second stage, they are now protomonts.
3. The protomont will travel to you substrate and attach to the surface, it will encyst and enter the third stage, it is now a tomont.
4. The tomont will divide into hundreds of parasites, the 4th stage, called tomites.
At this stage it cannot affect a fish, it is just laying around waiting around maturing, which usually lasts about a month. After this...
5. The tomites will hatch and are now called theronts. They will swim around and infect a fish once it finds one. Once they do they are called trophonts, beggining the process all over again. If they do not find a fish or host within a day they will die.
Your best course of action would be to put all your fish into a QT tank and medicate, either with copper or formalin. Let your tank sit for about 5 weeks and you should be good.