Aquatics Unlimited: Articles: Undergravel Filters Revisited
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Undergravel Filters Revisited

In the dozen or so years since we first published The Undergravel Filter Controversy, we have received a considerable amount of feedback from our customers and via the Internet. Most were supportive, and some raised a few issues not fully covered in the original document.

Is it really impossible to have a healthy aquarium with an Under Gravel Filter? No, of course not. Undergravel filters have been used successfully by many hobbyists, including respected experts, for a couple of decades now. The real points of our original article were that UG filtration is neither an absolute necessity nor without limitation and risk. We still stock UGFs and sell them occassionally to customers who have had previous success or just plain want one. On such occassions, we try to stress the importance of regular maintenance of the gravel bed.

Should I remove my existing UGF? Only if you are dissatisfied with it's performance. We're big fans of the old adage: "If it ain't broke, don't fix it!" If your maintenance routine plus an undergravel filter results in a clean, attractive, healthy aquarium, by all means keep doing what you're doing. On the other hand, if your aquarium seem to be forever in need of cleaning or has chronic problems with water quality or fish health, it might be time to consider switching to another style of filtration.

Why shouldn't one "just turn off" a UGF? If a UGF has been in operation for any length of time, solid organic waste may be in abundance in the gravel and under the plates. While the filter is running properly, these degrade aerobically into compounds like nitrates and phosphates which may be algae stimulants and fish growth inhibitors, but at least are not generally toxic. If water flow is halted, oxygen becomes unavailable in the gravel, and these same waste products break down anaerobically into much more noxious compounds like hydrogen sulfide and methane. If you choose to discontinue a UGF, it should be removed completely, and you should be prepared to deal with a huge release of organic waste. We recommend performing a partial water change immediately after removing the plates and rinsing or replacing filter media in the remaining filters several times if necessary.

Can a turned-off UGF function like a "plenum"? That's a tough question. Whether or not the "Natural Nitrate Reduction", "Jaubert" or "Plenum" systems will turn out to be a short-lived fad or a long-term institution remains to be seen. Their proponents, however, seem to be convinced that differences in plenum depth, gravel size and depth, and even the size of the screening can spell the difference between success and failure. It would seem unlikely that simply installing a UGF plate could just happen to fit the bill.

What about Reverse-Flow UGF? In theory, this looks like an ideal filtration system. Water is mechanically filtered first, hopefully by a good quality cannister filter, or at least by a foam block. The "cleaned" water is then forced down the UGF tubes, is distributed under the filter plate, then sort of percolates up through the gravel. This would, again in theory, address our major concerns with UGF: the accumulation of solid waste and/or gravel packing in the gravel bed. Unfortunately, practice appears to fall far short of theory in this situation. No matter how well pre-filtered the water appeared to be and whether standard UG filter plates or a custom bed was utilized, solid waste accumualted in the gravel, and it was very difficult to achieve a relatively even water flow throughout the bed.

So what are you recommending in filtration these days? We sell a lot of systems with one of the power filters with the rotating "wheel" plus an inexpensive sponge filter to bury in the gravel. The power filter performs mechanical and chemical filtration quite efficiently, and it's rotating wheel supposedly can perform as much biological filtration as an entire UGF. The sponge performs some super-fine mechanical filtration (clears hazy water) and sooths the nerves of those who feel they've got to have something down there under the gravel. We test water chemistry for many of our customers regularly, and again almost never see even a trace of ammonia or nitrate in such systems.

A final word. We would like to thank those who have commented or asked questions about our position on Undergravel Filtration - and especially those who have made the switch and reported success!


Copyright © 1998 James M. Kostich
All rights reserved.

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