Is the test kit Nessler based or Salicylate? Could be it's not meant for SW
use... Generally the darker the color, the higher the ammonia. Milky white or no color change would indicate a Nessler test kit. Yellow would be at the bottom of the scale with it getting darker (bluish/green) as the level of ammonia increases when using a Salicylate kit. Also be sure you are only referncing NH3
-, it is the only concernable value in SW
aquaria so be sure you are using the appropriate color chart as well.
Test kit age is definately a factor in accuracey.