You still have alot of bypass. You should try and bunch up all the sponges into one with a media bag or something so is one solid mass that fits snug on all the sides.
You could also get a rubbermaid tub(or anything to fit the barrel and pump in) and put the barrel into the tub. Adding just enough water to cover both the pumps and raise the bucket out of the water. Make all the media snug around the outside so there is absolutely no bypass. You have it setup so the water just runs right beside all the media. You want it to go threw the media. Its kinda like throwing a hotdog down a hallway right now
Did you look into the mattress pads, it would be great for mechanical filtration... Just cut a few round species about 1'' bigger than the barrel itself and stack them at the very top.
Ill try and think of ways to filter it the next time i go fishing