Ajar, getting back to the original topic of the thread. Hats off to you mate! That is a very slick idea. I disagree with taking the course sponge out of the top. I think it's an excellent idea as long as the air/water mix can flow through it. You can probably tune that with a needle valve anyway.
You just invented a combination wet/dry sponge filter... Congratulations my man! I'll bet that set up eats ammonia and nitrite like no other sponge filter. I have to build one myself.