A natural planted tank uses natural processes rather than high-tech equipment to achieve and maintain the desired plant growth.
The basic recipe for a natural planted tank consists of a soil underlayer, moderately hard water, a variety of plant species, and adequate lighting. A natural planted tank goes beyond that simple recipe, however, since the basic
recipe can apply to many planted tanks including aquascaped, high-tech tanks. Those beautiful high-tech tanks showcase phenomenal
growth of almost any plant species, but they bypass natural processes
and require considerable maintenance; in contrast, natural planted
tanks use natural processes as much as possible. For example, the
decomposition of organic matter by bacteria, not artificial CO2
injection, provides natural CO2. And fish wastes, not chemical
fertilizers, provide nutrients for plants and maintain soil fertility.
A soil underlayer is critical for a natural planted tank. It provides
CO2 to ensure good plant growth and provides nutrients exclusively
to rooted plants, giving them a major advantage over algae. Using
soils in aquariums can be problematic, however. The initial obstacle
for hobbyists seems to be finding the perfect soil, but there is no
such thing. Over the years, I used many soils that were probably
not ideal (e.g., heavy clay soils and heavily fertilized potting soils).
I incorrectly assumed that the more fertile the soil layer, the better
the plant growth. That said, these less-than-ideal soils settled down
after a few months and worked quite well for many years.
Commercial preparations sold for planted aquaria are generally
less well suited for natural planted tanks, as they are designed for
high-tech tanks with CO2 injection and fertilizer dosing and may
not contain enough organic matter to provide plants with sufficient
CO2. In a natural planted tank, bacteria digest the soil’s organic
matter and release CO2 into the water. Following the setup of such
a system, one can actually see the soil’s CO2 released in the form of
Unfertilized potting soils have given me the least initial problems
and the best long-term results. I now use a commercial brand of
organic potting mix that is readily available and contains somewhat
standardized ingredients. Because this particular potting soil is classified
as organic, it does not contain inorganic chemical fertilizers.
Chemical fertilizers can cause major problems in natural planted
tanks. For example, when a potting soil is submerged in water, chemicals
containing nitrate (e.g., potassium nitrate or ammonium nitrate) will
quickly convert to toxic nitrite.
1 Sulfate-containing fertilizers (e.g.,
potassium sulfate, ammonium sulfate, etc.) will convert to hydrogen
sulfide, a foul-smelling gas that can kill plant roots and endanger
2 Chemical fertilizers may work fine in high-tech
tanks, but they can cause major problems in natural planted setups.
The one fertilizer I sometimes mix with the soil is a bone meal mix.
It provides mainly phosphate and calcium in a slow-release, organic
form that probably stimulates root growth. I have never tested it
experimentally, however, and plants seem to grow fine without it.
The organic potting soil does not generate much turbidity,
thereby reducing the number of water changes needed during
setup. Moreover, the soil is more decomposed (composted)
than some of the generic topsoils sold by home supply stores.
When I used one of these topsoils, an oily slime developed
on the water surface at three weeks and a couple of fish died
precipitously. I suspect what happened is that the fresh wood
matter released some inhibitory oils (possibly cedar oils, pine
tar, etc.). In order to keep the fish safe, I had to change water
every one to two weeks for the first two months. Eventually,
though, the tank settled down and is now without problems.