My planted tank is (temporarily!) overstocked for a planted tank too.
I have a lot of debris building up on the sand too, but have always had this even when there were only 8 fish in it. The cause of this is my pair of Ancistrus chewing on the bogwood. I notice you have a couple of 'plecs' and they may be the cause of much of this.
Also the cichlids in my tank are responsible for putting some of this into suspension as they chew over the bottom, and i only have a couple of Nanochromis! Your Acarichthys (incredibly beautiful fish BTW!) and rams might be the other reason for suspended particles.
I reckon you could solve the problem though if you up the water changes (removing as much debirs as possible with a syphon) and add an extra, cheaper internal filter that you can run temporarily to remove the suspended debris. If you fill it with floss rather than the foam and then chuck that away after the cleaning it should help.
Long term though you might well have to cut your fish load a bit i'm afraid if things don't settle down.