Wow. Just read through the whole thing (at work, don't tell anybody). It makes my 4x8 deck pond look pitiful.
One question, though... I've been able to understand most of the ginormous filters used in the DIY section (especially nolapete and the Indy DIY guys), and I understood yours, until you started talking about adding air to the mix. Is that for normal operation or for cleaning or what?
If I could figure it out, it would be worth making something like that simply to rinse gravel out (like you did as a side effect).