your making H2S (hydrogen sulfide) inside your chiller hence the rotten egg smell this occurs when water is left to sit with no oxygen for too long first your culturing anerobic bacteria (occurs when no oxygen is present) once the anerobic bacteria run out of food (nitrates) the culture then dies leaving behind H2S which in turn is highly toxic to both you and your fish if the culture were fed continuosly all that would be left is harmless nitrogen but how to use this to our advantage is an entirely different story so what i am saying is leave the pump on full time so the chiller can continuosly and accuratley monitor the temperature and turn the heater on an off as needed as well as chill the water when needed the pump keeps the water temperature monitored at all times inside the chiller by supplying the chiller with your current water temperature to turn the pump off is defeating the purpose of continuous temperature management
