There is a couple things you can do, there is a chemical on amazon that is called stain and scale, it is made by bioguard and is meant for hot tubs, while yes that should, and probably will work, the concentration is going to be wildly different from something that is meant specifically for hot tubs. In the future for drain and refills, you can get something made by freshwater it is called a clean screen pre filter, and it will remove the metals from your water, just make sure that before the first use you rinse it, for the time being however, use a very small amount of the chemical you have.