Ok this is going to be 2 questions.

#1) I am going to be setting up a 40 breeder soon with the hawaiian black substrate. It is gravel like substrate. Not large gravel but not sandy. My questions is what is the best depth for this type of substrate? is it sill 4+ inches or because of the type of substrate and the fact it will serve to house different beneficial bacteria and critters than sand would, it would need to be shallower or deeper?

And #2) On my 125 gallon, my skimmer has been skimming like a champ. Pulling some stinky stuff. But lately it have been pulling straight porto-potty smelling skim mate. I lost 2 tangs in my move and restocked my tank with different tangs. But other than that i haven't changed anything in my tank. I still use the same fish and coral food water changes weekly. I am not complaining how well it is skimming. My concern is if it is pulling stuff this soupy out. What if it is not getting enough out or something is going wrong in my tank. Everything is still very happy in the tank. Corals are happy. All fish are fat and happy. Jusy being pre emptive about this as a cya. Too many peoples tanks have been crashing. I don't want to add mine to the list. Thanks in advance.