hello i have an aquaone aquastart 320, 40 ltr tank for shrimp and moss .the filter is a huey hung type sponge about 6" diameter. doing the job ok just looks big and bulky. so what do you guys recommend as a replacement ? wondering about external but the tank has a lid and is on the worktop in kitchen. cheers jon edit just looked at dennerl nano and tmc nano anyone use these?