Actually, my first thought was to put the sponge on the outside of the intake ... so that it sort of looks like a mini sponge filter. In effect, you'd be adding a small mechanical pre-filter.
I guess it would work on the inside, too, but on the outside it would be eaiser to clean (which I'd guess you'd have to do fairly often, maybe twice a week -- or maybe more, if you've got live plants).
As you've probably guessed, you've sort of got to walk a fine line, to make sure you don't impede water intake too much. But, if your AC 200 filter block is like the AC 500 filter block, I think a chunk of that sponge may be porous enough to let enough water in, and still protect your fish.
Here's the problem. I have a 29 gallon tank with an Aquaclear 200. The tank has been established for a little over a year. I had many accidents when the smaller fish would get sucked up into the filter. To resolve this problem and avoid more fish from getting trapped in the suction, I wrapped a net on the intake tube and secured it with small rubblerbands. I hoped the net would block them from getting pulled into the filter. 
Well, that helped a little but some of the fish were just getting sucked up and caught around the pipe. I added a small pastic ball (the kind that are used as bird toys) and slid it around the pipe. After my little African Frog had gotton his leg sucked into the pipe, I couldn't risk the other fish and my two other frogs. This time I wrapped the net half way up the pipe to be certain there were no little spaces which could allow something to get caught. 
The only probelm is that the filter doesn't have a strong suction and the water it isn't flowing very fast. The water is only dripping and I fear that the fish aren't getting enough oxygen, even though the aren't gasping at the surface. I added an air pump into tank, but what do I do about the filter? Any advice? 
No I really haven't thought of getting rid of the net because that was the only thing I could use that would keep my fish from getting sucked up. Now that you mention it, that would be a great idea to use a sponge instead of the net. Do you mean putting the sponge inside the intake pipe? 
