Before I get into the details, just remember the important motto: "Healthy plants = healthy fish." Plants are overwhelmingly positive contributors to fish health-- oxygenating water, removing poisonous substances, serving as medium for beneficial bacterial colonies, releasing anti-bacterial agents into the water, decreasing fish stress . . . the list goes on and on. As long as you can keep plants healthy, fish will thrive.
If you can keep plants healthy, they go a long way in "keeping things clean." they not only purify water, but also out-compete algae, preventing it from growing.
Generally, "decaying plant matter" is almost non-existent (or at least extremely minimal) in a dedicated planted tank, but animals like Amano Shrimp, Otocinclus cats and Siamese Algae eaters double-duty in both controlling the tank's minimal algae, and consuming old plant leaves. Also, if your plants/tank are truly healthy, a bit of decaying biological matter (like discarded shrimp shells or dead leaves) actually provides good additional plant nutrients.
I do a lot of maintenance for plant/fish care (dosing fertilizers, trimming plants, feeding fish, etc.), but the only "cleaning" I do are weekly water changes (about 20%-50% a week) and very occasional glass scraping.
Yes and yes-- you do have to use a filter, but you do rely on the plants to oxygenate the water.
First, the purpose of a filter on a planted aquarium is not to oxygenate the water (this is not its primary function even inside regular fish tank), but to create water flow and enhance biological filtration. While plants do eat up ammonia, nitrite and nitrate (in fact you have to dose additional nitrite/nitrate for them), a stable nitrogen cycle is much more easily produced with the inclusion of mechanical filtration with developed bacteria colonies for biological filtration. While cycling the tank is less important than in a fish tank, it is still highly recommended.
Now, I mentioned that the filter is generally not used to oxygenate the water in a planted tank-- that is because unlike in a fish-only tank, a planted tank cannot afford heavy water surface disturbance. Filtration is usually done with an external (canister) filter, with both the in-flow and out-flow outlets installed below the surface of the water to avoid surface turbulence. With no surface turbulence, plants must do the heavy lifting in oxygenating the tank (which, they actually do much better than surface turbulence).
Why no surface turbulence? Have you ever shaken a bottle of soda? If you shake water, you loose saturated CO2, and if you've ever taken basic biology, you know that CO2 is essential for photosynthesis-- ie. no CO2, no plants.
3 components are needed for optimum photosynthesis and plant health-- light, carbon dioxide, and a number of macro/micro nutrients (fertilizer). These things must be balanced inside the aquarium for plants to thrive.
Light is generally supplied in high-powered compact florescent lights (6000-10,000 kelvin). Unless you have purchased or built lighting specifically for planted tanks-- you don't have enough light. Your basic aquarium kit is hopelessly dull in supplying light. Also direct sunlight is generally a bad idea, as it is highly conducive to ugly algae growth and will make things a cleaning nightmare. Metal Halides are high-energy, high-power options often used by more skilled gardeners with high-growth tanks, but are also loved by salt water coral enthusiasts. Generally, that degree of intense light is unnecessary for beginners.
Carbon dioxide fertilization is essentially . . . necessary for the planted tank. Water contains very low amounts of saturated carbon dioxide (back to our soda example, CO2 escapes water very easily). In nature, aquatic plants either (a) live with flowing constant new water, or (b) grow "air" leaves out of the water (example: lily pads). Since neither of these options are available in the aquarium where the water stays the same and aquatic growth is used for the design, the water itself must be artificially saturated with CO2. Generally this is done with "pressurized CO2", a CO2 canister hooked up to a regulator (a mechanical mixer that blends CO2 into the water during filtration) or the more popular diffuser (which feeds directly into the tank, and creates a fine "mist" of CO2). I use the diffuser method. Fine mist means that CO2 bubbles rise slowly and have a lot of surface area-- optimal for saturation in water. With good water flow, the mist also makes direct contact with plant leaves, allowing the plants to absorb the bubbles directly.
Fertilization . . . well, there's all sorts of nutrients plants need, and all sorts of ways people dose fertilizers-- from pre-mixed products to direct measurement and dosage of laboratory "hard ferts." I personally go for the simplest methods available . . . generally, nutrient rich substrate is also used in planted areas of the tank.
Now that you have some idea of how things work, let's talk about the sexiness of this tank's system to illustrate how it works in the world's most massive planted tank:
So Amano's home tank, the biggest planted tank in the world-- it's measurements are 150cm x 150 cm x 500cm (~ 5ft x ~5 ft x ~16' 5")!!
The tank's specs for filtration, CO/fertilization and lighting are insane-- with that size, they have to be!
First the lighting system. Between 5 am to 9am, the overhead sky lights are opened to allow direct sunlight to come in. While constant direct sunlight is definitely bad, small doses of early morning sunlight are good for overall plant care (though is generally unnecessary). At 8:30, before the sky lights are shut, several florescent lights come on to provide the staple lighting, and run until 6:00 in the afternoon. The tank also has several high powered metal halide lights it burns for 2 hours of the midday. With such a deep tank, the lighting regiment is even more important, and it's incredible that Amano-san can grow this tank (with stem plants no less!) and not have any dying/decaying leaves or plant matter even at the lowest levels (with the least light) in the tank.
Now, if you look in the upper right hand of the tank, you'll see a glass box inside the aquarium. This is the "crash box" and is the outflow of the filtration system. It is actually a customized 15 gallon ADA rimless tank, that has been hooked up so that its rim matches the surface of the water. Teeth are grooved into the edge of the crash box to allow water to flow in between the teeth and into the crash box. Now, remember how I said that surface disturbance is bad for planted tanks? This is where the beauty of the crash box comes in. Water splashes down, turbulates, and gets oxygenated inside the crash box-- without affecting the CO2 saturation of the main tank! From there, the now oxygenated water goes into the filtration system.
The aquarium is actually constructed over a massive sump system, with several chambers used to treat water during the filtration process. Of course there are several chambers dedicated to your standard biological filtration, but there are a number of unique and plant-specific chambers as well! Of course, the sump is hooked up to automatically resupply water lost to evaporation, as well as do the weekly water changes. Fertilization of macro and micro nutrients is also carried out automatically inside the sump. There is also a chamber with an air stone used to further oxygenate the water. Next, a chamber with CO2 Reactor is used to churn in CO2 and re-saturate the water with carbon dioxide. Finally, the water is run through a UV filter (used to kill phyto plankton and microscopic floating algae species that cause "green water"), before being re-routed through the outflow pipes into the aquarium. A very high flow rate is used blow out trash (uneaten fish food or dead leaves) caught between plant leaves, and is also integral for fertilization/CO2 delivery, and also ensures activity and exercise by the fish.
Of course the tank is also home to approximately 1000 Siamese Algae Eaters, 400 Otocinclus catfish, and some 1500 Amano Shrimp, that play their roles in eating algae, uneaten fish food, and generally disturbing plant leaves/sand to free up debris to be picked up by the water flow/filtration system.
Yeah, a lot of the insanity described above is irrelevant to your average hobbyist (or even your average planted aquarium designer), but it demonstrates the basic principles-- and I figured if you wanted specifics on setting up more simple systems, you can ask me or better still: Go to an aquarium forum.
There are several planted aquarium forums that are wonderful sources of aquarium information. I don't go to them any more though because they have even more angst, drama and other annoying BS than smogon does! (incredible!)
If you want info/links on other sites, PM me-- I don't want to "advertise" on our forums.
