Last thursday i purchased two axolotls. They are in a 1m tank, (perhaps 20gallons?). with large pebbles, some pipe to hide in, rocks and two plants.

I filled it with tank water (no chlorine, i assumed bacteria would be established), and added sodium bicarbonate to achieve a pH of around 7.3.

I have a reasonably good filter, (500L/hour) which is attached via suction caps, and positioned for minimal flow, as to not disturb the axolotls. I also have an air pump.

Last few days i have noticed a powerful odour coming from the tank, though i have not left any food remains etc in the tank.

I figured this might be due to an ammonia build up, (though early, axolotls produce a lot of waste?) and so today i purchased some beneficial bacteria and aquarium salt. I added 20ml of beneficial bacteria, 1/3 cup of aquarium salt and did a 30% water change.

Will the salt harm the axolotls or plants at all? is there anything else i should do? any advice or criticisms appreciated.
Thanks
Does adding aquarium salt kill beneficial bacteria?
I only added the salt because the lady at the pet shop suggested it. She says she adds it to all the tanks, and said it wouldnt hurt the axies. Ill do another water change tomorrow.
Yes i have read through axolotl.org, and they suggest added salt if your water, as mine is, is soft:

http://www.axolotl.org/requirements.htm#hardness

Are you really sure it will damage them? its a very minute amount of salt in proportion to the tank size, (hardly 3 tbsp), and it was recommended by both axolotl.org and the aquarium lady.