The substrate of my tank is a wheelbarrow full of sand from Studland Beach taken at low tide near the water. An inch or 2 down and the golden sand is black with anaerobic mud - this is the good stuff! Studland sand is a fine golden sand which is possibly a little too light for the circulation I employ - its too easily stirred up and without the canister filter would have kept the water murkey. After several months its pretty stable and has a thriving population of worms and bacteria.
The nitrogen cycle takes place within this mud and unlike canister biological filters, wet/dry filters and undergravel filters whcih gradually raise the nitrate levels to high levels which are then almost impossible to lower a natural anaerobic mud bed breaks nitrate down to nitrogen gas which harmlessly bubbles to the surface. My sand bed is only 2 - 3" deep, ideally I'd have a deeper tank and a bed of 6 - 10".
Landscaping in the tank consists of a number of different rocks - all 'live', ie taken from below water and encrusted with life. I have some great chalk rock with beadlet and snakelock anemones, barnacles and bladder wrack. Chalk is an excellent rock for aquariums, its a great buffer rock for maintaining pH and hardness. As its porous its also excellent for natural filtration allowing a slow and steady conversion of organic waste to nitrogen in its anaerobic core.
Additionally I have flint nodules and Kimmeridge Shale. The Shale is thickly encrusted with Corallina officinalis and other pink calcareous algaes.
The foreground is largely sand, the back and sides are piled up with rock.
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