I'm always a big fan of: If you don't know if you should add more, or less of any chemical, add less--except for chlorine--add more.

But powdered chlorines are not just chlorine, so I like the "go slow" idea.

The whole point is if you put too much of just about anything in your pool you have to now do something else to fix it. If you put in too little, you add more.

Except for bleach. Too little you get algae (BIG bad!), too much you may bleach your liner (little bad), if you have a liner.