Hi I just wanted to ask a quick question about filters, are they needed and why, I was thinking about having a small circulation pump like they have in ponds, I only have a 97 ltr tank with guppies, and they do love racing in the stream of the pump, and I know it produces tiny air bubbles, but is it really needed? Can an underwater circulation pump work just as good less noisy too, I already have an air stone so airy that enough for air