No turmoil - in my mind

by Frank G Anderson

There are several disadvantages to the undergravel filter, none of which should preclude most hobbyists from using one. In my mind, the undergravel filter is probably the best buy on the market. The disadvantages include weight. At a general guideline of about 1 pound per gallon, a 55 gallon aquarium will have at least 55 pounds of gravel.

Another "problem" with undergravel filters is that they do collect waste, microorganisms, and a whole gambit of other particulate and chemistry that can be detrimental to your aquarium. Undergravel filters can also cause damage to aquatic plants. These filters are also maintenance-intensive to some degree. I would recommend an annual 100% tear-down in certain cases. See comments below. With these disadvantages, why would anyone use an undergravel filter? Because they are the aquarium's workhorse. I have used undergravel fitters for over three decades. In some situations, they are not desirable, but in most, they are. They can be used as main filters for either marine or freshwater tanks, with, of course, different media in one (crushed coral for marine, silica-based sand/gravel for freshwater).

Some of the arguments recently sounded against the undergravel filter are gaining a bit more credibility than they used to when they cropped up because today's external filters are becoming more utilitarian (multi-purpose), more compact, and more efficient. They are also somewhat more expensive than they used to be in many cases. The biggest argument might be financial. When you can buy a 55 gallons undergravel filter plate set for $17.99, why should you spend $118 on an external canister filter? You may ask. The answer is found in whether you get the same thing or more out of one than you do with the other. The answer is found in maintenance of either. If you maintain, or simply, take care of the undergravel filter regularly, it will do all you want it to and more.

Undergravel filters work on the principle of using relatively fine crushed gravel particles suspended over a perforated plastic plate to process water that passes through the gravel constantly. The water usually passes downward partly through gravity, partly by aid of air pumps that draw additional water up through the gravel and back over the surface of the aquarium water. I say usually because there's the reverse-flow undergravel filter that causes water to be forced upwards from the bottom of the gravel up into the main tank compartment. I believe that this is, in principle, scientifically at odds with Mother Nature, but that's another story. Presuming that we are discussing the more common regular-flow undergravel filter, the water passes downwards into the gravel media, where it is partly inhibited by the gravel and turbulence. In addition to its flow being inhibited somewhat, the actual physical and chemical nature of the water undergoes change as it passes through this filter media. Why?

Because the gravel media grows two main types of bacteria. One is anaerobic, which helps break down the ammonia wastes in the tank generated by fish. The other beneficial bacteria type is aerobic, which further breaks down the ammonia-now nitrites into nitrates. Combined with regular (est. two weeks at 25% volume) water changes, this chemical breakdown and water recharging dilutes most of the poisons in the water, making your aquatic environment relatively safe for your fish. Well, if you are still shy of the undergravel filter, at this point you might be asking can't the external filters and these new gizmos do the same thing? Well, yes they can, but consider the size and thus the volume of the undergravel filter. A 55 gallon tank is about 4 feet long and 1.5 feet wide, or 6 square feet. Multiply that by about .5 for the est. 6 inches of gravel, and you come up with a volume of about 3 cubic feet. How much would you have to pay, and what kind of maintenance would you have to keep up, one external filters of that volume? The price is right for the undergravel filter.

The disadvantages I mentioned earlier included an annual 100% breakdown. This would consist of actually removing all the plants and decorations from your tank, then the fish (providing them with sufficient aquarium water from their normal home outside the tank), and finally most of the water. Then you would scoop out the gravel and wash it in clean tap water in a plastic bucket under the outgoing stream is clear. With your other two hands (!) you can clean out your tank and filters. OK, after all this, you can reinsert the undergravel filter plates, put the gravel back in, and slowly, carefully put back in the plants and decorations, then the fish. What's wrong with this picture? The one thing wrong is that with major maintenance such as this, most or almost all of the beneficial bacteria that resides in your gravel filter has been destroyed or washed out. What do you do now? Keeping in mind that not all of the bacteria will have been destroyed, you can observe and monitor for the next month to ensure that your fish will have a safe recovery. The level of nitrates and nitrites will rise for the short term, and this could guarantee that you will need to make at least once or twice a week 25% or more water changes. Still don't like this picture? Well, another way of dealing with this 100% breakdown is to provide a practical alternative. Remember, you are not trying to destroy your gravel efficiency, only to clean out some horrible messes and prolong your fish's life and plant health. You could, as an alternative, siphon out the gravel with an aquarium siphon on a regular basis, which should be the case. For that annual maintenance, instead of the 100% breakdown, why not just trick your undergravel filter into taking a bath? Undergravel filters are notorious for collecting very fine debris under the filter plates. That's what usually forces these 100% breakdowns. But you might not need to go that far. After thoroughly siphoning the gravel itself, cover the inlets/outlets to the undergravel filter plates, except for two which should be as far apart as possible. On the one, place an extended tube to allow the water to drain out, hopefully into the garden or patio. On the other, place your water pump and using inlet water from the aquarium, allow the pump to force water down into the one inlet and thus force water under the gravel filter plate out the other end. This may take a few minutes, but it will remove all or most of the fine sediment gathered there at the bottom. Which was the purpose of that 100% breakdown.

A brief description of the siphon mentioned above. An aquarium siphon is just a piece of plastic tubing, some 12 inches long and maybe 3-4 inches in diameter. It has another piece of tubing, perhaps an inch or less in diameter and 3-4 feet long, attached to it. In siphoning the aquarium gravel, the hobbyist would do well to attach that small diameter tubing to a garden hose, so that the water will drain directly out of the aquarium, avoiding a bucket on the floor, to the garden. Place the siphon into the tank, and suck on the far end of the outlet to cause a vacuum that will draw water from the tank out. A better and more hygienic method is to have enough water in the hose so that when you place the siphon into the tank, and drop the hose end, the resulting drop will force the water out the hose, causing a vacuum behind it that will then draw the water out of the tank. Keep in mind that the pressure of water leaving the hose end will increase dramatically with higher levels between the outlet end and the tank inlet. Knowing this will provide some caution, as you don't want too much suction that will draw out the gravel and fish and plants!!

This routine of vacuuming the gravel - I follow it about once a month on the average, increasing when needed if I have been negligent, or feel that the fish need more water changes and the gravel might be starting to deteriorate in efficiency because of a lack of maintenance.

This is just a brief look at the undergravel filter, and I hope it is enough to convince you that not only is the UG filter not dead, it is very much alive. If you want to keep it so, here are five tips.

1. Keep the filter relatively clean, vacuuming it once every two weeks or so.
2. Keep in mind that the nature of the gravel itself can and will affect your water parameters, including pH. Regular darker gravel might, for example, help keep a pH of 6-7, while a lighter colored one, based more on sand, could help drop your tank pH down to 5. Is this what your fish want?
3. Keep at least 4-6 inches of gravel over the top of the filter plate.
4. Go ahead and use plants with the UG filter, but you may have to place the plants over a "dead area" prepared over the gravel plate.
5. Supplement the undergravel filter. This can be an occasional outside canister filter treatment, or one on a regular basis, or use of a box filter, or two sponge filters. Filtration is an important part of aquaria, and fishkeepers should not jump the gun for or against any particular method until they find what works for them.

As with any advice, this is also somewhat subjective. Experts don't always agree, and frequently disagree on major basic scientific aspects of the hobby/business. But I trust that the above will help you make a more informed decision, and that it will result in better fishkeeping on your behalf.

Frank G Anderson tongmuan@loxinfo.co.th