I just salted my tank with aquarium salt, I am just curious if this will kill off beneficial bacteria?

Nope, it shouldn't really affect your beneficial bacteria if you're just salting to add electrolytes.

I'm not sure at what level, but you might kill them off if you had SUPER SUPER SUPER high salt saturation. As long as you're not dumping a whole bag of it into your tank you should be fine.

Thanks... I added 2tablespoons per 10us gallons in my 12gal tank.

*runs through the measurement in her head*

I think that's a good amount... Heh, I usually go at it "1 teaspoon per gallon" so I don't get confused.

I am pretty sure that's what it said on the box.

I have a few little tanks at my mum's house, so it's easier for me to work with a measuring system for tanks less than 10 gallons.

Approximately:

1 Tablespoon per 5 gallons OR 1 teaspoon per gallon = 0.1% salt
2 Tablespoons per 5 gallons OR 2 teaspoons per gallon = 0.2% salt
3 Tablespoons per 5 gallons OR 3 teaspoons per gallon = 0.3% salt

All are for level spoonfuls of large grained aquarium salt.

Awesome conversion summary Daryl! I'll have to save that for future reference. I'm always losing track on the right amount of salt!