Depends on the pH of the water. If it's < 6.5 pH, there won't be any issues at all with small doses. As the pH climbs higher and higher, a larger percentage of the ammoniacal nitrogen will be in the form of NH3 (ammonia), which will cause problems.
One must consider that the bacteria in the tank will convert some portion of the dosed amount (of ammoniacal nitrogen) into NO2. This is also a problem.