How to build a Plenum to establish Anoxic conditions in your aquarium.PART 2. Using sand.

How to make a very slow moving water Plenum with sand substrate. Great for planted tanks, too.

In a slow water moving Plenum you only want about 1-2-gals of water to be exchanged through the Plenum a day. Sand compacts because of its very exceptionally small particulate matter and moving water too fast will cause this compactness of the media to escalate and lessen its porewater and permeability abilities to the point that anaerobic bacteria will predominate the media.

By moving water very slowly from underneath the sand bed Facultative bacteria will predominate the substrate and because oxygen will not be depleted in the sand bed, it will stay anoxic in nature and not go anaerobic.

I have been using this same method for the past 25-years, after I realized that placing sand or and very fine media directly on the bottom of the fish tank only led to ammonia producing anaerobic bacteria turning the substrate black on the very bottom.

There are two ways to stop a sand-bed from going anaerobic on you and that is through a moving Plenum or only making the sand bed 1" deep and making sure that some kind of fauna becomes part of the ecosystem in the sand-bed itself.