An Aquaclear 110 is an excellent choice! If you are concerned about the smaller fish you can slow the flow down by moving the intake tube to the right. The idea of putting a sponge over the intake is a good one too. The sponge for the Aquaclear 70 is a good one to use. These filters are very versatile and you can add carbon or floss or anything else you prefer. Reuse the sponges over and over by washing them out in a bucket of tank water.