I recall that when I started fish keeping, there were basically two choices for filtration: under-gravel filters and hang-on backs. There were also expensive canisters for people with large setups. When I visit Petsmart and Petco, I find few options for under-gravel. They just sell a single one-side product, I think only suitable for a 10-gallon tank. Why is it so rare to find these nowadays?
People consider them obsolete.
Under gravel filtration is an old technology, and seems to be going out of favor for newer types of filters, to the point where under gravel filtration has become a point of controversy among people who keep aquariums, with many arguing that they should no longer be used at all.
The arguments against them seem to boil down to:
- They tend to get clogged over time.
- They are inconvenient to clean, sometimes requiring a teardown of the tank.
- Newer types have better filtration.
- They aren't good for growing live plants.
However, it seems not all of these arguments are necessarily true. For instance, the problem with clogging can be prevented with proper cleaning, and not overpopulating the tank with fish, and not all aquariums necessarily need something more complicated. There are also other points in the under gravel filter's favor, such as it being cheap, simple, reliable, and since they are largely hidden beneath the substrate, they look nicer than many other filters.
Under gravel are cheap so the dealers have made them "politically undesirable". I expect in fresh water , depending on fish density, type, and food ,etc, the gravel may need to be cleaned . I found them to be great for salt . With aragonite/crushed coral/limestone gravel the water flowing down through the gravel picks up calcium which is necessary for water chemistry. My calcium stayed at 500 ppm and I never added kalkwasser ( calcium lime water) which is required without a undergravel filter. And all sorts of creature live in the gravel and eat debris. I enjoyed taking a flash light when it was dark and watching the activity in the gravel. I never cleaned a UGF in salt water. Unfortunate I have not seen (larger) live animals in fresh water gravel.