That substrate has been in place over 25 years and has never dried out nor been deep vacuumed of the original mulm. The rust brown crap is slowly getting worse with time. It looks more brown than this pic shows. You can see where the otos have been chipping at it.
I got the bundle of manzanita branches fully saturated and now I need to take it out of the soak bucket and arrange them into an interesting shape using nylon wire ties to hold the branches in place. Then I'll use SS screws to lock it all together. The wire ties will come off just before it goes into the tank. I'll give it another soak day to get some more tannins out.