I dont understand the problems with the different sizes of substrate.
Do not get me wrong I have experienced it too.
This is what I did (both bad and good)
120:
Put origional substrate in and put rocks on top.
Had fine particles all over it for months.
Constantly blew off the rock during cycle.
Would go in and move sand around to get rid of drifts/dunes. (even as the tank was cycled and was active)
180:
Placed rock and then put in sand.
Started flow during cycle with a 900gph pump set on angle to just move the water around.
Moved some of the orig sand dunes to level out sand. (That is why in my last pic you can see some substrate lines)
DID not touch sand after it all settled out.
Added oolite, orig substrate, fiji pink. At different times.
I do not have any thing that will move the sand. I have snails, brittle starfish. but no gobies or anythnig that will move the sand around from one palce to another.
I have even had an anemone and it's host clown move sand to attach to the bottom of the glass. So YEAH there is a large divit around one anemone, from the clown moving sand.
I am not saying my tank is perfect or there is some magnet under neath it. I just lket it find it's own place and it has stayed there.
The flow is currently produced by two mp40's that ramp up to 80% at different times during the day. I set it to ON which is 100% non fluxuating at least once a week for up to 30 minutes.
The heads are about 6" from the surface and are pointed AT each other with only a 2" latteral difference. This give a bounce off effect that creates eddy's in current not only on the surface but is seen through out the tank. I have them on both sync and anti-sync patterns. They run an hour pattern then switch.