The loading (F/M value) effect the efficiency of organotrophic and nitrifying bacteria

Dear all,

1.One of the inflows is stopped because of the regular inspection, and the COD loading is decreased, but the NH3-N loading is the same. The COD reduction rate is keeping about 90%, but the NH3-N reduction rate is decreased from about 90% to 0%.
(1)the wastewater is decreased from about 18,000 M3/D to 11,000 M3/D.
(2)the inflow COD change from 1,000 ppm to 700 ppm.
(3)the inflow NH3-N change from 20 ppm to 40 ppm.
(4)the MLSS of activated sludge is decreased from about 3,000 ppm to 2,000 ppm.

2.We think,
(1) the loading of COD is decreased, the MLSS is decreased to keep the F/M ratio, so the COD reduction rate could keep the same (about 90%).
(2)The MLSS is decreased, the nitrifying bacteria in the sludge is decreased, but the NH3-N is increased, so the NH3-N reduction rate is decreased from about 90% to 0%.

3.Does someone have the knowledge or experience to assist to check our hypothesis, and help us to make the next step, thanks.