How long do you think it takes for an unopened bag of potting soil to completely nitrify? I ask because I recently purchased a bag of MG potting soil for cactus with a view towards just letting it "age" until I need it in the future. Is that a practical step to take in conjunction with mineralizing?Looks good! Those stem plants look happy. I think reducing water level was a good move.
Nitrites will come down and source of problem probably is nitrates in the bagged soil. I am pleased to hear that you have alluded to nitrate respiration. Excellent! I addressed that in another thread just a moment ago.
Soil particles are negatively charged and they attract positive charged ions (Ca++, NH4++, K+, etc). And they repel negatively charged ions (anions) like nitrate (NO3-) and nitrite (NO2-). So your nitrite problem will disappear rather quickly as these anions diffuse out of the soil.