And what will happened with this big amount of OC (let say ethanol) dosed for a month until we are waiting for this lazy anaerobic denitrificators to start working? Except fish being constantly drunk and with hangoverYes but still in tanks with high NO3 levels (over 50 mg/L) I have seen down going of phosphate but not any significant down going of the NO3. After around 3 - 4 weeks (without any WC. PO4 adding or so) but still the same DOC dose - a fast down going without any signs of cloudiness or raised amount of skimmate (large bacterial biomass) Clearly this fast down going has not been related to bacterial growth.
DOC is one of the most valuable compounds (if not The most) in the nature there is little chance to stay unconsumed for months waiting for anaerobic denitrification to kick in.
Denitrification bacteria need phosphate as much as the other bacteria to grow and multiply if there is phosphate limitation it will limit denitrification bacteria to grow too.