Read this-
http://www.mankysanke.co.uk/html/trickle_tower_update.html
What is discussed on this site is a true Trickle Tower not a modified trickle bed filter. This loose and interchangeable use of names is what leads to problems. Two people may be using the same name for describing a subject but in reality be discussing two completely separate things. The devices being labelled Trickle Towers on most internet sites are anything but a true Trickle Tower. This happens all of the time in the world of Horticulture with common names for plants. It is so bad, that horticulturists use only the Latin names to avoid any confusion.
The purpose of a Trickle Tower is to reduce Nitrate levels. This can only be done by facultative heterotrophic bacteria. In the presence of Oxygen, these bacteria consume organic Carbon by using Oxygen as the catalyst. In the absence of Oxygen, these same bacteria have the ability to utilize Nitrate for the same purpose, producing not only Carbon Dioxide but also Nitrogen gas in the process. Nitrate levels are steadily reduced through this process. Providing Oxygen by any means nullifies this process producing no reduction of the Nitrate level.