I'm really confused about this. Sometimes I hear all you need for a pond is a pump/fountain. Some people don't even use that and just have plants for oxygen. But then some use filters... is this just needed for small ponds? Do larger ponds NEED filters? I'm getting a 257 gallon stock tank and in March/April when its warmer I'll be putting my goldfish in it. I'm going to add plants too and get a pump.. will I need a filter or not? If I have rocks/bricks in the bottom can good bacteria grow under it like it would in gravel in a tank?