I've been using this enzyme stuff I got at the hardware, Drano Max ("Build-up Remover"). It's not the old powder-pellet draino, which is NaOH (lye), but is gentler, easier on the pipes and not caustic. Liquid in a 1/2 gallon plastic bottle. I don't follow the directions, though. I use less, am more patient with it. Generally put in a couple of ounces, a little warm water to spread it a bit in the clog and let it sit for hours before using the shower again. After a few of these the water flows freely in the shower again. Repeat when necessary. If that didn't work I'd pay a visit to my tool lending library and get a snake.