Rays are pretty much impervious to prazi, as far as I've seen. I've never gone above a x4 dose, I think, but I haven't ever seen any reaction to it at all. It is best to know what you are treating a ray for, before you treat it, but that is just to save you the time and money. Prazi is pretty much the safest thing you can do for your ray, except for maybe salt and slightly higher temperature.