Have a look at koiphen forum if you haven't already. Several members there have done what you intend to do.
At the heart of the nexus is a static bed for easy clean mechanical followed by a moving bed of K1. A lot of people (including myself) use 2 separate barrels to accomplish the same thing.
Thanks for input Fellas.Outstanding thread; very interesting! Looking forward to updates.
The cheapskate DIY-er in me is now wondering how I can build one of these out of Rubbermaid bins and garbage cans...
How is the mechanical media cleaned? I see the waste valve to drain sediment, but the actual media must become steadily more and more clogged as time passes. Is that inner chamber easily removed and just pressure-washed to clean, or does the media need to be removed and washed separately?
The conversion that I'm doing is not unique. It is a kit that Nexus put out as a product improvement for their Model 310 with full instructions.
People have complained that the center mechanical chamber is too close to the bottom making it difficult to wash. They've raised stainless steel chamber off the bottom allowing full access underneath and introduced K1 micro to trap more particles.
This looks like a very easy filter to maintain. That and applying this to fish other than Koi is my main goal.