I have a Oase Biosmart 36000 filter system with a uv 36w and a aquamax 12000 premium pump.Three and a half thousand gallon of water with 20 small goldfish and two small koi. I don’t know what l am doing wrong as although the water perimeter is ok and l clean the nine sponges weekly as it needs it, l notice a fine sediment on the shelf and sides.Do you think l should add another filter bix onto the the Biosmart if that’s at all possible with a finer sponge to hopefully catch the sediment or upgrade it.