oh god here we go again with undergravel filters...ANY knowledgeable LFS guy will tell you the negative FAR outweigh the positives with those artifacts...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..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 MOST fishkeepers try to avoid...If you polled everyone here UGF users would be far in the minority, and theres a reason for that..Sure they work for some people, but EVERY other kind of filter is better in all of the important aspects, facts are facts. If you have the means, avoid ugfs they are dinosaurs