w,
You should always wait 24 hours after you initially add a large amount of salt to your pool before you turn on the cell..
"...a little low" does not really tell us much... if you added the salt 24 hours ago and your salt level is above the minimum required for your cell, then fire it up...
Most cells just don't work at all when the salt is before their minimum level.
How are you testing to ensure the salt level the cell says you have, is close to the actual salt level in the pool?
Thanks,
Jim R.