Free Ammonia Calculation
Key to the colors in the computed result: Green is ok. Orange is ok for a short period. Red is hazardous.
The calculation is based on James Alleman's formua (step 11 of reference 3, below).
I have not found general agreement as to the exact free ammonia levels for a particular degree of toxicity. My best guess is shown in the colors. See the references to make your own refinements.