Did Janet scare you enough? I hope so. Muriatic acid is dangerous stuff. It's cheaper, and once diluted, better for your pool, but it's dangerous.

On the other hand, it's not nearly as dangerous as gasoline, so it's not a big deal if you handle it correctly. Writing a muriatic acid page is on my to do list, but it will be a week or so. Three other tips you might want to keep in mind:

#1 - The fumes are bad to breath, but they are death on wiring. Do NOT leave even capped muriatic acid in your garage or pump room, unless it has EXCELLENT ventilation, like TWO open doors. Instead, store it outside in an old plastic garbage can or bucket. If you do store it inside, put it in a HD plastic trash bag, and close the bag tightly. When you need to use it, take the bottle and bag out TOGETHER, and open the bag outside.

#2 - Once you have opened the bottle, and removed the inner seal (sharp stainless kitchen knife -- RINSE blade promptly in pool) you can easily pour and avoid both fumes and splashes IF you will partially submerge the bottle in the pool, take the lid off and set it on the pool deck, and then tilt the bottle so that you pour into the pool with the bottle's lip only a few inches above the pool surface.

#3 - Guesstimate doses; do NOT try to measure them. If you try to measure acid, you WILL have bad fumes, and you WILL eventually spill some. Don't do this. Instead, figure out your approximate dose, and the pour about that amount or less directly from the original container. If in doubt, pour less: you can always add more later!