I recently joined this forum and was somewhat surprised by the number of hobbyist who dislike undergravel filters. I have had a conventional one in every tank since the 1970's, and since this adds up to dozens of undergravel filters over several decades, I thought I might be qualified to clear up a few concerns. I only went to reverse flow a week ago, (Thanks for the advice, Bryan!), but can already explain some amazing benefits of this set-up too. This is my opinion based on many years of experience and I am entitled to it. If you feel otherwise, don't flame me. Instead, post a response expounding your own experiences and let the readers decide for themselves.
From what I can tell, the most common undergravel concerns are: 1) They are "old technology" and have out-lived their usefulness in the hobby. 2) They offer poor filtration. 3) They are not suited for growing live plants. 4) "Muck" collects underneath them and is impossible to remove. 5) They clog up constantly, fouling the tank and creating maintenance woes or killing the bio-mass of beneficial bacteria. 6) They are hard to clean.
In the same order, here are my responses:
1) They are old technology for sure, but this alone is a ridiculous reason to avoid them. The latest, most expensive and complicated solutions are not always the best answer to life's simple problems.
2) They do offer very poor mechanical and chemical filtration, but when properly maintained the biological benefits are huge. And remember, biological filtration is the most important and the one you can never have too much of. In conjunction with a good power filter, they do offer worthwhile benefits.
3) I am not a horticulturist, neither in gardens, pots, nor aquariums, so I wouldn't argue with this except to say that not everyone cares about it. That most all tropical fish will thrive in unplanted tanks with 3 different types of filtration (biological, mechanical, and chemical) along with regular partial water changes is an established fact. I prefer the look and convenience of artificial plants, and undergravel filters are fine for this. I also enjoy replacing my expensive bulbs only when they refuse to light up - about every 5 years and sometimes much longer.
4) Totally agree, but not a problem with pre-filtered, reverse-flow powerheads.
5) Not if kept clean. And again, not much of a problem at all with pre-filtered, reverse-flow powerheads. These push only filtered water through your undergravel filter solely for the benefit of biological filtration and do nothing to clog the substrate. Indeed, the reverse flow option may even keep gravel cleaner than using nothing because it discourages floating debris in the tank from settling in it.
6) Hogwash. Until last week I had used a conventional undergravel filter in every tank I have owned (about 25 total) for well over 30 years, and sometimes nothing else. And as long as I did not over-feed the fish, the gravel only needed cleaning about once a month and could be stretched to twice that in under-populated tanks. This is done during bi-weekly water changes and adds no extra time to this simple responsibility. All you need is a bucket and a simple, inexpensive gravel siphon. Coincidently, the siphon tool actually makes scheduled water changes much easier and is probably something you will want to own anyway.
I have a theory that undergravel filters earned their poor reputation in the past, and mainly for symptoms relative to a fault which I have never even heard discussed: Conventional ones did encourage over-feeding
, especially if there were bottom feeders in the tank. Any food that was targeted at bottom feeders was quickly sucked into the gravel and out of reach of the hungry fish where it fouled the filter media (gravel) prematurely and caused maintenance headaches. The lowest fish starved though plenty of food hit the bottom only to disappear into the gravel. I learned quickly it was better not to keep bottom feeders than to foul my undergravel filters trying to get enough food to them. For this reason I have had a decades-long happy affair with even conventional undergravel filters, though I am certain most aquarists continued to over-feed and hated them. Again, the advent of reverse-flow has totally eliminated even this problem for attentive aquarists.
Though I have done it many times and for years at a stretch, I do not recommend using undergravel filters as the sole means of filtration. Canisters and power filters are just too inexpensive and good these days to not have one on every tank - at least for primary mechanical and chemical filtration. (I prefer hang on the tank power filters for their unmatched ease of cartridge maintenance and lack of hoses and connectors.) However, unless you want live plants rooted in fine, fertile substrate, adding a reverse-flow undergravel filter to an already good freshwater system does make it better.
Look at it this way - You already have gravel in the bottom of your tank and it should be cleaned occasionally anyway. Why would you choose not to circulate a supply of clean, oxygenated water through it for the benefit of critical biological filtration? This is probably the largest surface area in the tank. It seems a shame not to use it as anything more than decoration.
Sponge filters seem to be all the rave these days and enjoy much praise for their superior biological qualities. But they are UGLY, and take up waaay
too much room in the tank, at least in my opinion. And they must be regularly removed from the tank and replaced, or at least rinsed and squeezed out in a sink, totally disrupting the bio-mass. Not so with an easier-on-the-eyes undergravel filter. It remains inside the tank forever - even during cleanings - with it's bacteria mostly in tact, so there is much less chance of harmful toxins ever spiking and killing your prized fish.
And one more thing concerning undergravel filters used in conjunction with power filters for extra biological filtration - they can be run with a cheap, battery operated air pump during power failures. This has saved my fish more than once. During an interruption, power filters stop and their bacteria quickly die off, but undergravels can be kept in emergency service rather cheaply.
Listen, aquariums need all the biological filtration they can get. You can't go wrong by adding a simple, effective, undergravel filter to your fish's life support system. And they do have their benefits over other types of filters. The more I research other methods, the better I like my undergravel filters.
Hope this helps somebody.