Sponge filters are great for fry tanks not only to be able to keep your fry in the tank ratehr than sucked up into a HOB or canister but also for the fact that the fry can graze on the microorganisms in the sponge between feedings
You really only need the sponge on the intake tube. This is only for the babies protection. (Although the post about fry eating off the filter is a good point).
thats what the plants are for lol.... you could get a sponge filter with a power head. if you have a internal filter already you could mod it to use it.