The ozone/UV light sterilizers work, but it has to be really, really over the capacity of what you're probably looking at., not any of the little ones you can buy, which wouldn't give you the protection you're looking for, they would be in multiple hundreds of $ range, rated for the 150+ gallon capacity. plus they have maintenance costs.
Its much cheaper to quarantine your fish for ich, and prevent it from getting in, in the first place. Other pests like cyano, dinos and green water can be controlled if/when the problem arises.