Hi I've had a 330l coldwater tank up and running for about 8 months. I have an external filter (Eheim Pro 3e 2078). I've never cleaned the filter yet, and according to the service button it won't need cleaning for another 6 months! Would this be right? I've never used an external filter before and had problems with cloudy/green water which has finally gone crystal clear (praise the lord!) I don't want to mess about with the filter unnecessarily for fear of messing up the water again but I also don't want to knacker it by not servicing it!