Hi, tank has been re-vamped about 4 weeks ago changed the stones on the bottom to smaller ones, the tank is 1200x450x450 everything was going fine untill i changed the stones, I have an underground heater on it well under the tank that is and the temp is around 24 degrees, it has the tank that is being running fine for years .... a mate uses the same small stones and his plants are all looking good, I got mine off him ...lol