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Free Ammonia Calculator
Enter Total Ammonia:
Temperature   PH > > > Table of Free Ammonia
C F 6.6 6.8 7.0 7.2 7.4 7.6 7.8 8.0 8.2 8.4 8.6 8.8 9.0 9.2 9.4
 
    0.0 is ideal. Values up to 0.019 might be tolerated for extended periods
    0.020 - 0.049 may be tolerated, but will cause long term harm
    0.050 - .0.199 May be tolerated for a few days, harmful
    0.200 - 0.499 May be tolerated for a day or two, very harmful
    >0.500 Extremely Toxic, remove fish

What is 'free' versus 'ionized' ammonia? Free ammonia (NH3-N) and ionized-ammonia (NH4+-N) represent two forms of reduced inorganic nitrogen which exist in equilibrium depending upon the pH and temperature of the waters in which they are found. Of the two, the free ammonia form is considerably more toxic to fish and, therefore, we pay considerable attention to the relative concencentration of this particular contaminant.
Existence of these chemical species are generally viewed as indicators that a given water has been contaminated, usually in relation to the direct discharge of an ammonia-bearing waste (e.g., fish waste, uneaten food, rotting leaves, something dead in system, etc.).
Just how toxic is free ammonia? The U.S. EPA's criteria for free ammonia toxicity are presented in terms of system pH and temperature for both total ammonia and un-ionized ammonia (NH3) according to both 1-hr values and 4-day averages. The U.S. EPA recommends that these levels should not be exceeded more than once in three years...which would enable a system to recover from the stress which would have been caused by ammonia pollution. This approach implicity recognizes that some degree of fish mortality is acceptable.
For aquaculture systems, published recommendations are as low as one-tenth of the U.S. EPA's recommended concentrations in order to avoid killing fish.
Notes:The formulas used here are based upon work by Professor James E. Alleman, Purdue University
I'm confident this calculator is accurate, but things happen. Use it at your own risk,