things I didn't know about water softeners

Today I learned that if you unintentionally neglect your water softener by not cleaning the resin for, like, ten years, when you finally get your act together and clean it, your water can run black afterwards for more than an hour (so far). It's gross, and it smells kind of yucky. I can't communicate the smell, but have a picture of my sink:

If you were wondering, that pipe is the drain for the second washing machine. (I still have a second washing machine because of my laundry issues, and it drains into the kitchen sink because of course it does.)

The reason we decided to clean the resin was that after we would come back from being away, the water would always run brown for a little while. We bleached the iron bacteria a few years ago, so we kind of ignored it until now. The internet said to try cleaning the resin, and here we are.