Thanks for pointing it out Ed, I think it was a language barrier problem, and I just don't know enough about this subject, my excuses.
Jwerner, the description: "When setting up a new fresh water aquarium, Supa Tonic Salts are ideal, or they can be used to condition the water for fish originating from areas with natural brackish water. It can also be used to combat fungus and other diseases and as a sterilising solution. If you are looking to hatch brine shrimp eggs, then Supa Tonic Salts can be used to create ideal conditions" made me think it should make a tank relitively safe. If there would be a safe product that would do a proper enough job, I'd think I would use it. With proper enough, I mean it would kill off all bad things that are likely to appear in a tank, just to make the risk smaller. I think I'm just worried about using something potentially harmful like ammonia or bleach, and I'm not educated enough about the risk of every single bad 'germ' in the tank.