If there is a distinct smell coming from the reactor then it can mean one of two things

• The reactor is due to be cleaned and the bacterial mulm has built up limiting water movement inside the unit. Please see the unit instructions for the cleaning method.
• The redox in the unit is too low. This can be caused by the water flow being too slow or excess nitrate fluid going in to the reactor. Increasing the water flow through the unit slightly will usually resolve this.