The grey stuff you're referring to is "Ammonia absorber", I've used it before when I've had an Ammonia spike due to adding too many fish too soon.
You'd like "Nanoreefs" - small reef tanks(I've got a 15 gallon tank set aside for just this), that don't have filters at all - just a regular small waterchange, more to replenish the minerals the "live rock" needs. All they generally have is some intense lighting, and a powerhead for circulation. All they usually have in them is a single clown, which looks kinda odd with 50lbs or more of live rock in the tank.
I just realized that I have no active setups, yet have something like a half dozen tanks, as well as stands for two more(30"x12" and 72" x 18")
HTRN



