Feel rather stupid with questions like this, but I'd rather be safe. Setting up a new 20h .... First time aquarium...... Rinsed the gravel really well in a bucket until water had no debris of any kind..... When I put it in the tank the top has some tiny gravel pieces on the top of the water. I am a little concerned about it and the filter(penguin 150). Second question was how close the heater should go to the filter .... Fluval 200watt. Any help would be much appreciated.