I have been hearing a great deal of talk over the last twenty years or so about how you should not use undergravel (UG) filters, especially with planted aquariums. I am very suspicious of this talk. I have been using undergravel filters since 1960 and almost all of those tanks have been planted. I have never had any trouble with any of those tanks except for the first one, and that was because those early filters only had 1/2 inch lift tubes, so they had very small flow rates and deadly anaerobic bacteria could easily find pockets of no flow to grow in. Once the makers shifted to 1 inch lift tubes, the problem was eliminated. I have always had excellent plant growth in all of my tanks. I suspect that the main source of these tales is people with a vested interest in selling expensive canister filters and sump systems. There is no doubt that these systems, once set up and established, are really top value, and for fish that constantly move the substrate and short circuit the biological filtration of a UG filter, they are indispensible. Goldfish and cichlids are very bad about that. However, for the average hobbyist with little money for fifty to two hundred dollar filters, here is a system that works almost as well and costs much, much less. That system includes a simple hang-on-back filter and a UG filter equipped with a powerhead. In my experience, there is no system for biological filtration than an UG filter. My reason for believing this is based on the time required to cycle a new system. When I hear highly experienced people talk about cycling canisters and sumps, they almost always say that it takes something close to a month to cycle their tanks. Using UG filters and checking ammonia and nitrite daily, it has never taken me more than a week. If I mix my gravel with a handful of gravel from an established tank, I can bring that down to two to three days. The big argument that I hear against UG filters is the muck that accumulates under the filter plates. It is ugly and It smells bad. This muck is a mixture of fish poop, uneaten food, and dead leaves from the plants and is undergoing a process of bacterial and fungal decomposition. Aquarists call it mulm. Gardeners have another name for the same thing when they find it. It is called compost. Gardeners eagerly seek out garbage (uneaten food), poop (manure) and all sorts of plant matter, gather it together in huge heaps, and let it decompose for months, with the end result being a wonderful addition to any garden soil. The same thing happens in the UG filter. Why is this a good thing? Dead leaves, fish food, and poop contain huge amounts of all the minerals required for plant growth, and I do mean all, including trace minerals unknown to scientists. But there is a problem. These minerals are in a form that plants cannot use. They are insoluble. Plants can take in only nutrients that are dissolved in water. In order to convert this solid waste into soluble plant food, it must undergo decomposition and the best way to do this is through the action of fungi and bacteria. In order to do thus with a minimum of bad smell, we need for the decay to occur in an medium rich in oxygen. This condition exists in the gravel and under the plates of a UG filter. If there is an excess of decaying matter, it can pile up on top of the gravel. That is why we have gravel vacuums to remove the unsightly excess. The mulm below the plates is harmless. it is slowly but surely being reduced to a soluble state where any excess can be eliminated by regular water changes. Another benefit of an UG filter is exchanging oxygen and carbon dioxide. Most aquarists know that plants need carbon dioxide during the day to perform photosynthesis, and with high light levels, they can use up the available CO2,l leaving the water oversaturated with oxygen in a process called pearling. What most people don't realize is that plant roots produce large amounts of co2 at all times and need oxygen for healthy growth. A UG filter sucks the CO2 rich water up from under the roots and draws oxygen rich water down through the gravel, nourishing the roots. So, to recap, a UG filter encourages the decomposition of mulm and circulates the resulting nutrients throughout the water column, while evenly distributing CO2 and oxygen throughout the water column. (NOTE: With a UG filter There is no differentiation between the substrate and the water column in regards to nutrients. The water column moves freely through the gravel bed, carrying nutrients to all parts of the tank, including the plant roots. As proof of this, you will see no dead brown roots with an UG filter the roots are uniformly white.) Now to speak of the Lee filter specifically. There are other UG filters available, and I am sure they are very good, but I have personally used Lee filters since the seventies and have never seen any reason to seek out any other brand. They do the job and do the job well. I highly recommend them to any person who wants to use a UG filter in their tank.
