Early graphs such as this one, using data published by Liao in 1972, began to define the proportions of free ammonia (NH3) in comparison to ionized ammonia (NH4) when varying temperatures and pH were taken into account. A reasonable knowledge of mathematics was required to understand them and to work out the acceptable level of total ammonia for koi at different pH and temperatures.   Life became a little easier when this table was published by Spotte in 1979. It still needed a slide rule to work out what would be a safe level of total ammonia. (A slide rule would probably have to have been used because, although pocket calculators were invented in 1966, the first practical ones were not patented until 1974 so they were not in common use until much later).   pH oC   6 6.5 7 7.5 8 8.5 9 0 250 77 24 7.7 2.4 0.78 0.1 5 154 50 16 5 1.6 052 0.07 10 105 34 11 3.4 1.1 0.36 0.05 15 74 23 7.5 2.3 0.75 0.25 0.04 20 50 16 5 1.6 0.52 0.18 0.04 25 35 11 3.5 1.1 0.37 0.13 0.03 30 25 8 2.5 0.8 0.27 0.1 0.03   When tables, like this one from OATA, began to appear, life became easier still. To find the maximum acceptable value of total ammonia, it was simply necessary to look up the pond temperature on the left and the pH at the top. The value where they intersect is the maximum level of total ammonia that can be allowed under those conditions.   There was, however, one remaining problem. With respect to those who have published tables like the one above, they were designed for ponds and aquaria of all types, not just for koi ponds. Koi would not be feeding at 5oC and would be dead at 0oC, so the top two rows of values are of little use to koi keepers.  Also, since the recommended range of pH for koi is 7.0 to 8.5, the other columns of pH values are not relevant either.  Only the highlighted area is strictly relevant to koi ponds and quarantine tanks.  Because these tables cover a wider range, they can only give limited values in the area that koi keepers would like to see. For example, look up the maximum acceptable value for total ammonia for a typical koi pond where the pH is 7.3 and the temperature is 18oC. Those two values of pH and temperature do not appear in the table so you have to choose the nearest. You have to choose between 7.5,  5,  2.3 or 1.6, which one would you choose? The actual maximum allowable value is 2.99.  (Call it 3.0 and no-one will split hairs). As is repeated in the main article - with due respect to the authors of the other general ammonia tables, I have gone back to the original research and recalculated a new table that gives the maximum acceptable value of total ammonia that can exist in a koi pond.