Let me start with a really simple tweak which will greatly improve the performance of your Nexus.
As shipped, at least with the old 200 units, the air lines have very fine (~1mm) holes drilled for air. These are on the upper surface, presumably for ease of drilling 'in situ'. Small holes make sense - if a user is using an under powered air pump you still want all of the air ring to bubble and don't want still areas around the back of the Nexus as no air is getting there. Also, small holes mean small bubbles which are better at increasing oxygenation.
However, small holes on top have 2 issues....
Firstly, when you switch the air from outer ring to inner ring to clean the Eazy in the centre, the tube starts to fill with water. Some of this is expelled when the air is switched back on, but not all. Over time, the dark slimey bacterial film we are so keen to promote in our ponds (and on our K1) starts to build up inside the airline and eventually, will block the airholes.
I have found over the past 7-8 years I have had to drain the Nexus probably once every 3 months to clear the airline - a tedious job with a cocktail stick and a slightly painful one, lying across the top of the Nexus and hanging down to reach inside to prick the airline....
In the photo, you can see the Evolution Aqua original airline with the small air holes blocked by bacterial slime and the new airline I have fitted, with 2.5mm air holes. You can make the improvement without taking the air line out - you just lean in with a cordless drill (having 1st emptied the Nexus of water and then swept the K1 around to the other side of the unit) - but it is much easier if you take it out and has the advantage that you can put it back in the other way up, with the holes facing down - so any water ingress will be expelled when the air is turned back on.
(Turning it upside means that you cannot unblock it without removing it - but hopefully, you will not need to with the larger holes).
I have to be honest and say that I have not had this modification running long enough to make a scientific comparison, but I have no dead spots whereas, with the same air pump I would get them within days of pricking out the old air line and also, when I drain the Nexus and scrape to the bottom of the K1, it is all clean whereas before I was quickly building up a layer of mulm at the bottom due to the lack of agitation or flow below the airline.
So sofar, so good - I will update this post with any additional news on this mod as it becomes available.