Good morning! I've been following along and thought I'd add my two cents worth. Our bog is an above ground long skinny affair. A pipe with saw cuts in it sitting on occasional bricks on the bottom runs about 2/3rds the length then turns up with a 90 degree elbow to the surface with a cap on it. The pipe is covered with about two feet of pea gravel.
The bog is three years old and has always had a layer of "mud" on the surface. If I open the cap all I get is clear water and I can see where the water percolates up through the gravel with the cap installed.
The plants thrive to the point I have to cull them a couple times a season. My thoughts are; if the bog collects the "mud", the "mud" isn't in the pond - if the plants are so prolific they have to be thinned out - and if the pond water is clear, the bog is working.
We have tads, (both toad and frog,) living in there which are pretty good harbingers of the health of the system.
If your bog gets "dirty", it's working.....