why place filter under the gravel in aquarium?

Answer 1

The filter is placed under the gravel to create a water flow through the gravel. This introduces oxygen into the gravel. The surface area of the gravel then becomes a substrate for good bacteria to grow and break down the waste produced by the fish.

Answer 2

Evidently a lot of people have the basic theory on under gravel filters right,but nobody knows how to maintain one.When doing water changes the gravel should be "vacuumed",using something like the Python-No -Spill-Clean-and-Fill. system,a very handy,but overpriced tool. As the siphoning process is done,the gravel is sucked up with the "stuff" contained in it,(into a large diameter plastic tube) the rate of siphoning is varied so the heavy gravel swirls around in the tube,while the lighter waste goes up into the siphon hose, and down the drain.If this is done weekly (you do change some of the water every week,don't you?) the gravel won't get stopped up with waste,the waste won't build up under the filter plate and the fish will be happy and healthy. All that being said, I wouldn't depend solely on an U/G filter alone,outside filters provide a good way to introduce things like charcoal bags and other filter media that are difficult to use with an U/G. Also it's good to have a second or third bio-filter going in case one fails and for this the U/G is very reliable if cleaned regularly. Some U/G users clean only half of the gravel at a time so as to have an undisturbed bacteria bed at all times,personally,I believe that it's more important to clean the gunk out. Finally, another important item with any bio-filter system is oxygen,the beneficial bacteria all run on oxygen,and will fail with out it. Air stones or filters that disturb the surface of the water will work just fine. The important thing is to break the surface tension of the surface. Good luck,have fun with your fish. PeeTee

Answer 3

The undergravel filter It's basically a plate that covers the entire bottom of the tank, on which you place the gravel. Then an airpump or powerhead is used to suck the water through the gravel, using it as biological filter media. This works great, but unfortunately these filters don't remove any of the solid waste and instead suck it deeper into the gravel and under the plates, where it's very difficult to clean out. They work fine to keep fish alive, but they're not very good filters, all in all, as they build up waste and degrade water quality in the long term.

Answer 4

Well, the underground filters require the least maintenance. Those ones that hang outside the tank have charcoal and a cotton like filter. You have to replace those materials quite frequently. The underground filters don't have anything, its just a big piece of plastic with some holes in it. There job is too pull the fish crap down through the rocks and get it trapped at the bottom of the tank, under the underground filter. From there they just decomp naturally, but don't pollute the water.

Answer 5

undergravel filters are the perfect breeding ground for the "biologicals" that you need to keep your tank healthy. These bacterias are need for keeping waste levels down. The increased surface area in your substrate , with the oxygen moving across it (via the undergravel filter) are very benificial.

I have to say that being said , undergravel filters are not completely necessary.

I have two external filters and an undergravel in my planted 40 gallon tank.