I have a 20 gallon tank with about 12 very small fish. I want to upgrade the existing HOB filter and need help deciding between a good HOB filter such as the Aquaclear 50 (or similar) or a small canister filter such as an Eheim classic or a Fluval 06 series. I also would need some sort of protection on the intake tube so my small fish don't get sucked into the filter. Any advice would be greatly appreciated.