That's the thing, obviously the heavier the particles or rather the greater their mass, the easier and quicker they settle out.
The water entering the LLH will suddenly go from being in a faster flow 15 or 22mm pipe or whatever, into a much larger bore vessel, that's when settlement will occur to a certain degree as you're finding, just like we get settlement in our sumps in similar circumstances.
I've looked all over for research papers, that I can read free, to get a real scientific conclusion on settlement factors and limitations but not found many. Most are on waste water industry research, often on specific issues rather than a full breakdown of the whole process.
Obviously waste water industry applications are closest to pond and aquarium applications as they're trying to achieve same objectives, getting as much suspended organics and detritus of all sizes out of the water.
For that the longer the dwell time the better, then in my case it's over to the skimmer/skimmers to do the rest of the physical removal prior to further breakdown, then we're into biological after that.
Like I said previously this is a mission to achieve as much physical filtering as possible without a physical barrier, ie without floss or socks etc.
One thing would like ideas on is what to build my display around, ideas on a postcard please
You see I don't intend putting any LR or rock in general in my display, all the LR will be in my sump so it is totally removable and "cook"able to swap pieces in and out over time easily.
So something non-porous and reef safe that you may find lost to the sea, maybe even stuff that either recently or in history may have been shipped in wooden crates
Ideas so far are large glass bottles or demijohns right the way through to a missile
anything that coral might colonise if lost to the see in favourable conditions 🤔