There are the Frog cartridges (designed to work in conjunction with minerals in another cartridge) but they are about the most expensive way possible to put in chemicals and are wasteful packaging.

I use one of these https://www.amazon.com/Life-Chemical-Chlorine-Floating-Dispenser/dp/B00B9CHBK0 with standard Br tablets. Adjust the opening based on the readings, once you find the sweet spot it's just a matter of replacing the tabs when they shrink down.

I do take it out when using the tub so it's not annoying.