Quote from James M. Kostich.
The risks of UG filters. If all else is perfect - if the fish are not overfed, if circulation is not hindered, if the tank is not medicated, and if the gravel is cleaned frequently with water changes - success can be achieved using UG filters. We stock UG filters and power heads mostly for those experienced hobbyists who have had previous success. Unfortunately, in most cases, something is less than perfect. Usually, after a few months of operation, the gravel begins to pack with so much silt and dirt that circulation stops and the bacteria suffocate. Since the filter still appears to be working, water quality deteriorates, usually unnoticed until it is too late. If the tank is medicated or overfed, an even more rapid die-off of the culture may occur. A speedy water change may avert disaster, but this is the sort of headache and frustration we are trying to spare our customers.
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I believe, this is not a referral of DSB set up.
In a DSB, we understand that bacteria that convert nitrogenous waste to harmless nitrogen gas are anaerobic. this means they live in conditions with no oxygen.
i guess this article is not reffering to DSB, and we assume/ believe that Ed Neo is not going to set up a DSB in a 2 full main tank too.
Hopes this article by James M. Kostich helps us understand better on UG and thanks for ur enquiries.