My wife was in Africa for a couple of weeks and took our Nikon D610 camera on her trip. While I missed my wife, I also missed the camera!
Hahaha.. I hope your wife doesn't frequent these forums as she may take your comments to imply that you missed the camera more than her ;-)
This thread is absolutely incredible and highly inspirational! Photos are stunning. Build is extremely well planned. Details + Photos are super helpful for an anxious newbie like myself -- in particular, your step by step breakdown of drilling the ATO and converting it to a refugium. I've thought of doing that for a long time but couldn't find anyone else who had gone that route. It seemed like an obvious option to me, but with nobody else doing the conversion I figured maybe it was just too small.
I'm thinking of going a slightly different route which is to incorporate flow coming from the manifold rather than a PMUP (as I find it annoyingly loud). The manifold would extend into the refugium and feed into a bar along the bottom to generate the flow for chaeto tumble, similar to what you have.
I bought a second pump for the manifold because I feared that the main return wouldn't generate enough flow back to the DT, and it seems like you might be running into exactly this problem. In my case I also wanted additional pressure to divert some of the flow to a spray bar type design using RO piping along the bottom of the sump to keep detritus off the bottom and in suspension. ie somewhat self-cleaning.
Please keep up the excellent posts, they are highly informative and your photos are absolutely jaw-dropping!