Actually ICH is caused by a parasite that is either free floating int the water or has settled onto things like plants
And if you kept up with WC's they wouldn't be there. (as much, you get my point)
Ich is so widespread that many experts feel that it is present in the environment of most aquariums, especially in larger holding tanks, rearing ponds of breeders, collectors, and wholesalers. In fact, just about every aquarium fish will come into contact with this protozoan at several times in its life. Because it is so widespread, most fish have developed a good immune response against the disease to allow them to fight off the protozoan infection before it ever causes any symptoms. Captive fish that develop ich usually get the disease when their immune systems are not functioning as well as they should be because of stress. We know that stress lowers the immune response and when fish are stressed that is when ich is most prevalent.
There are many causes of stress in a fish's life, many of which can be made worse or better by the owner. Water temperature, water quality, tank inhabitants, improper diet, and a variety of other factors all contribute to stress, but one of the most severe causes of stress occurs during shipping and handling of a new fish. Whether coming from the wild or farm-raised, the handling and shipping of the fish from their origin to a wholesaler, then to a retailer, and finally to your home is extremely stressful. With the widespread prevalence of ich, it is no wonder that many newly purchased fish are affected.
BTW here is the ich lifecycle:
The life cycle of
Ichthyophthirius is complicated but very important in understanding the treatment and prevention of ich. Once the ich protozoan attaches to the side of the fish, it begins feeding on the skin and tissue causing irritation. The fish's body begins to wall off the parasite to try to limit its damage. The protozoan continues to move around in the cyst feeding and growing, while the body continues to further encapsulate and wall it off. This encapsulation by the body is one of the reasons that ich is so difficult to treat during this stage of the disease because medications cannot penetrate through the wall of the cyst to reach the ich parasite. During this stage, the ich protozoan is called a trophozoite. The trophozoite eventually matures and is termed a "trophont." It will burst through the cyst wall and then fall to the bottom of the aquarium. It then begins to divide into hundreds of new ich-infecting units called tomites. This stage is very temperature-dependent within its capsule, with the fastest replications occurring at warmer temperatures near 78-80°F. At optimum temperatures, the replication will be completed in about 8 hours. At lower temperatures, the replication takes longer making the treatment time for eradication much longer.
Once the replication is complete, the trophont bursts and releases the newly-formed tomites into the water. The tomites are motile and swim around the tank searching for a fish to attach to. Once they attach to a fish, the cycle will start over again. It is during this stage that ich is most susceptible to treatment. Many of the available medications will kill the tomites, thereby stopping the cycle of ich in your tank. It should be noted that these tomites will only survive for 48 hours, if they do not find a fish to attach to. These tomites will also attach to plants, filter material, etc. So if you move a plant from an infected tank into a clean tank, you have just infected the clean tank with ich. Depending on the water temperature, the whole cycle can take from 4 days to several weeks.
