Aromatherapy salts shower attachment?

[jimjam v]

I've heard of an aromatherapy bath salt ball that attaches to any existing shower head, but don't know what it's called or where to find it. The idea is that you can unscrew this attachment and fill it with your own bath salt & essential oil mixture to be dispersed while you shower. I've found a similar product, but it uses these cartridges that need to be replaced. The unit I'm looking for does not take any sort of replaceable cartridge that you have to buy.
Any guidance on what this product is called would be appreciated.
Thanks