In my new (1 month old) FOWLR set up, I put 30 lbs of LR and for a
substrate, I put 40lbs of aragonite sand and 20 lbs of live sand. I can
now see two distinct layers in the sand. A layer of white about one inch
deep with a gray layer below it. I've seen pictures of tanks where the
two layers represent the aerobic and anaerobic bacteria at work. Have I
unwittingly created a "sand bed"? (not complaining if I did)

And a second question: With this much LR and LS, and running a skimmer,
do I need additional filtration, assuming I maintain a reasonable
bioload? Let's say 6 3-4" fish and 5 or 6 assorted shrimp/crabs/snails.

I currently have an Aquaclear 300 running just to provide mechanical
filtration.


Thanks,
Mark