The tried a true UG, there's a lot of love hate relationships with these filters and it is the filter a lot of people started with, at least before the other styles became cheap enough to compete.
.View attachment 181506
This filter consists of 1 or more "plates" that are placed obviously underneath the gravel. 1 or more lift tubes can be attached and then usually connected to an air pump. The airlines create a bubbling effect <more if an air stone is in the tube> drawing water through the gravel bed and into the uplift tubes back into the aquarium. Some people will attach power heads to these tubes making this filter much more efficient.
Reverse Flow Undergravel:
You can also install power heads that will pump the water from the tank down the tubes and up though the gravel bed from underneath. This known as a Reverse Undergravel or Reverse flow UG. Most advanced Aquarists prefer this setup as efficiency in increased vastly and the prefilter sponge on the power head keeps the plates underneath clean and debris free, This is the method I would recommend if someone wanted to go with the UG filter.
Your Gravel bed will act as mechanical and biological filtration as the beneficial bacteria colony will setup home in the gravel bed and under the filter plate as well. Debris and detritus will be pulled down into the gravel bed where it gets broken down.
The filters are extremely efficient and very inexpensive, and if a few basic chores are kept up these filters will last a very long time, however they do suffer some drawbacks. These filters require meticulous cleaning of the gravel bed surface and herein lies their biggest drawback...If you clean the bed you must be extremely careful not do go to deep as you will vacuum up all your Biological bacteria and force a recycle. You must gently disturb the gravel bed and get what comes loose and leave it at that.
These filters have a nasty tendency to get overloaded quickly usually as a result of a recent gravel cleaning. However once established and going the load these filters can handle is quite remarkable being so simple in design.
Keeping live plants in a Tank with an Undergravel is difficult <impossible with some species> and depends on the kinds of plants you wish to have. Other than potting them I wouldn't recommend this style filter if you plan on having a fully planted tank.
Hope I didn't miss anything if so put it up here.
Not true at all...bacteria are attached to surfaces....even the most robust gravel vac will not remove them.
 
	 
	 
 
		 
 
		 
 
		 
 
		
