Hi John, err I'm going to be rude, as this thread has grown massive since I was last here and i dont have time to read what i missed just now, so I'm going to post and if this has already been discussed, sorry!
I have been thinking about how you said the feeding of the bacteria works, and it seems a bit of a pain to measure nitrates and adjust the feed, I didnt understand whether you decided to remove a certain amount of nitrate daily and just added the equivalent amout of food (ie checked monthly) or you had to check daily. I was reading that there are two types of denitrifying bacteria that can be used in denitrators, heterotrophic bacteria that require a source of inorganic carbon or food and auto trophic bacteria that require a source of inorganic carbon...ie CO2...
If you have to adjust the level of organic carbon you add regularily I was thinking it could be worth adding CO2 gas instead, thus growing autotrophic bac, as it is cheap, and you could overdose the filter with it, but agitate it out with an airpump before it goes back to the tank, thus avoiding water quality issues caused by unused organic carbon...