By Alesia Benedict
Year to you all! I hope that one of you New Year's resolutions was either to set
up a planted tank or to try your hand with my favorite fish -- Discus! In this
issue of Conscientious Aquarist, my column will be devoted entirely to the
substrate for planted tanks. In the next issue, my column will talk about
various substrate options for keeping Discus fish and we'll explore some of the
lesser-known "Do's and Don'ts" of keeping these magnificent underwater beauties.
Planted tanks are unique in many ways,
and their needs differ greatly from just "fish only" tanks. One of the major
differences is the substrate required. While a few aquatic plants don't even
need a substrate, most do of course- and some even need very specialized ones.
Substrates serve not only as an anchoring method for plants in which to root,
but also as a vehicle for taking in nutrients. For some plants, a substrate is
absolutely essential for the plant to reproduce. "Okay," you might be thinking,
"so why can't I just pop down to my local aquarium store, purchase some pretty
gravel, plant some plants, and bingo, have a happy ending? After all, I'll be
purchasing the gravel in a fish store, so it should work fine for my
Well, not really. At least, not exactly.
What I mean is, not for a planted tank. The primary problem with that
"pretty gravel" that you purchased at the fish store is usually pebble size.
This may not matter much to fish, but it certainly does matter to your plants'
roots. Pebble matter that is too large will allow water to flow through it too
easily -- taking nutrients with it, and allowing debris to collect too easily in
the gaps between the pebbles. It also makes it difficult for the plant roots to
easily spread through the substrate. On the other hand, substrate with too fine
a composition can compact, restricting nutrients from reaching the roots and
causing damage to the plants.
The "just right" size is pebble matter of
1-3 mm with a rounded shape. Sharp-edged substrate, no matter how pretty, can
damage roots (and fish!) and should not be used. The depth of the substrate is
another key factor. I learned this the hard way when first working with some
Sword Plants (Echinodorus sp.) I had planted Sword Plants in one of my
tanks, and for a while, they were doing great. Yet, just when they got to a
certain size, the leaves began to substantially deteriorate and the plant looked
like it might be dying. In theory, everything seemed "right" within the tank,
but looking at the sword plants, I knew it wasn't. All of the other plants
continued to do very well, but the sword plants were now failing. I started to
experiment with the lighting, the fertilizing schedule, the water chemistry,
etc. all to no avail. In desperation, I decided to move the plants before I lost
them. As I gently uprooted the swords, it became obvious to me that the problem
was the roots -- they had become tangled, therefore not taking in proper
nutrients. They didn't have enough room to expand. In short, the substrate
wasn't deep enough! I significantly increased the back third of the tank's
substrate and replanted the swords. They prospered! An added bonus was that my
Crypts (Cryptocoryne sp.)
-- another long-rooted plant -- also took off. In my larger tanks (90 gallons),
the depth now slopes from a low of three inches in the front, to just under five
inches in the back.
Heating cables like these stay hidden
and protected under substrates while they mimic natural temperature
gradients between the substrate and water. Photo by Anthony Calfo.
Trying to simulate Mother Nature within a
little glass box is not so easy. In nature, the beds of rivers and streams are
usually warmer than the water. Sometimes this is only by a degree or two, but
even so, it is enough to create convection currents in the substrate. These
currents slowly but consistently circulate warm water up from deep in the
substrate (hence, slightly warming the roots) and then back down after being
cooled by the body of water. This current means that nutrients are always being
delivered to the plants' roots. Heating cables were devised to slightly heat the
gravel, keeping roots warm and creating a convection currents. While I don't
have any such apparatus in any of my planted tanks, some aquarists find them to
be useful when using thin layers of nutrient-laden substrate. This is a great
example of how Mother Nature has got this "plant growing thing" down pat,
whereas we humans scramble around trying to simulate it via technology.
A note of caution!
Gravel (and tank
decorations for that matter) with a high calcium content
should be used, which means leave the limestone
or coral based products on the shelf. This includes -ack!- all of the beautiful
sea shells you've collected over the years while vacationing at the shore!!!
Such items will increase the pH and alkalinity, and your plants will surely
suffer. So what can you use? Actually, as you'll see, you have numerous
choices, and there are pros/cons to all.
This gravel comes in a bunch of colors
and shades and is perfectly safe for all aquatic life. It is limestone-free,
contains pebble sizes of 1-3 mm, and if you push your fingers into it, it yields
effortlessly which means that roots can easily develop. If you have a tank in
which you are going to have deep-rooted plants, quartz gravel alone will not
typically be enough, as it is a completely inert substrate. However, I have used
it as the sole substrate material in two of my planted tanks which house
Vallisneria and shallow-stem plants. The plants are "fed" through water changes
(mineral traces), fish waste, and left over fish food (both which contribute
organic matter). This is enough to feed these plants' roots, and I add nothing
to the tank.
Sand has been used extensively in planted
tanks over the years -- and with good results. If you want to use sand, make
sure it is safe for the aquarium. Some commercial sand has traces of lime, and
we've already learned plants don't do well with lime-based substances in their
tank. The most common and well known sand used in planted tanks is "silver
sand". Many aquarium shop owners swear by it. However, really fine-grade sand
can compact over time and become anoxic. This can be lethal to aquarium
inhabitants, so I suggest that fine sands be added over a layer of gravel.
Aquarium plants rooted in an artificial
nutrient rich substrate. Note the reddish color from high iron
content. Photo by Anthony Calfo.
These substrates and additives can be a
huge blessing if you are cultivating deep-rooted plants or those that need an
iron-rich substrate. Heavily planted tanks, and/or a tank composed of "high
maintenance" plants may also benefit. The two additives that are most commonly
used are peat and Laterite. Peat is rich in organic matter and provides plants
with a high dose of nutrients, which can work wonderfully under ideal
conditions. I tend not to recommend peat as a substrate additive, because it is
tricky and under less than ideal conditions, algae can become more of a nuisance
than ever imagined. Laterite is a time-honored additive, and it is mostly found
in fine powder form. One can either mix it to the very bottom section of the
gravel, or layer it very thinly, with a sizably deep portion of inert gravel on
top, which prevents the Laterite from leaching out into the water. Another way
to get Laterite and other nutrients into the substrate is through the use of
fertilizing tablets. These tablets are pushed directly into the gravel,
typically on a monthly basis.
Over the last several years, plant
specific substrates have come onto the market. Flourite, Floramax, Eco-Complete
and Flora Base are some examples of these. My experience has mostly been with
Flourite, and I have been quite happy with the results, though I have also used
Eco-Complete with good results. I do not have first-hand experience with the
other aforementioned substrates, but would welcome feedback from readers who
have. These substrates work by releasing nutrients over a very long period of
time, continually feeding plant roots. When I use Flourite, 90% of the substrate
is Flourite, and the remaining 10% is simply a neutral-colored quartz gravel
layered on top. This top layer helps to show off the fish as well as keep the
"dust" down when planting and re-planting.
Sterilized potting soil (not regular dirt
from your garden!) can be and excellent choice for part of a planted tank
substrate, but it is very, very tricky. Care must be taken to choose potting
soils that are void of fertilizers and/or additives. Potting soil is very
rich in organic material and the tank will often go through many changes in
water chemistry while the tank settles. About an inch deep layer of potting soil
should be laid and about an inch of quality gravel laid over it. One important
benefit is that there is an ongoing breakdown of organic matter which results in
the continually low level release of CO2. Hence, CO2 injection, substrate
additives, fertilizers, etc. become unnecessary in many of these aquariums.
There are several downsides to potting
soil substrates. The aquarium can experience nutrient release spikes which can
be very dangerous to fish. This is especially true for the first few weeks
following set up and for this reason, fish should not be added for quite some
time. Filtering with carbon is also often required. Also, for aquarists who like
to move their plants around a lot (as I do), this is NOT a good option for you
as the soil will be kicked up into the water column routinely.
Now that the substrate is laid, the tank
is planted, the fish are swimming and all is well. What should be done with the
substrate in terms of maintenance? Leave it alone? Vacuum it? Vacuum only the
top? Well, it depends. UGH! I know I hate it when someone says that (tell me
the right method!), but it really does depend the tank. For the most
part, the substrate should pretty much be left alone -- resist the urge to do
dramatic things to it if all is well. In time, organic matter will collect in
the substrate and create anaerobic conditions and make the substrate more dense.
In a non-planted tank, this is reason to start freaking out, and a good gravel
siphoning is in order. Yet in a thriving planted tank, the organic matter is
going to be broken down and taken in by the plant roots, which will in turn
release small doses of oxygen into the substrate and prevent it from stagnating.
If, like me, your planted tanks have some
areas of gravel showing, then I recommend siphoning/stirring the top layer,
because mulm can accumulate. If, as in most cases, there are no plant roots at
the surface, it is best to remove some of the debris from this uppermost layer.
not, however, dig the siphon into the gravel to suck the substrate clean! In
my early planted tank days, I did this in a spot or two and I was horrified at
what the siphon was removing! My mistake was that I was applying the principles
of a fish-only tank to a planted aquarium. I have since discovered that it is
only when that "dirty layer" starts to become quite visible that the plants
really start to take off (it appears about an inch or two below the substrate
surface, and you'll actually see the layer). I do still siphon, but more to
remove mulm, dead leaves, etc., than to try to suck the life (literally) out of
Until next time, keep it underwater!