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> I have two tanks, both with the cheapest gravel man
> makes("filter media" in paper sacks). In my first
> tank, I added laterite because the LFS insisted that
> this was absolutely necessary. For my second tank, I
> decided to skip that step. And I haven't been able to
> tell a difference with my largely stem-based plants.
> Additionally, I haven't come across a plant that has
> failed to thrive. One difference my two tanks
> probably have compared to most is that they both have
> undergravel filters (not used anymore), not that that
> should make a difference.
Your tanks don't give you much basis for comparison. Laterite provides
the plants with little more than iron, and it may not do much of that
unless your substrate is anaerobic and/or has a low pH. Further, the
undergravel filter below the substrate may effectively prevent your
substrate from achieving conditions where the iron in the laterite is
available to plants. And still more, if you're adding chelated iron to
the water column then iron in the substrate may be completely
It isn't surprising to me that you see no difference between these two
> My personal theory is that mulm creates enough surface
> area for nutrient exchange that other substrate
> additions like laterite and soil are not necessary
> given that sufficient iron is added to the water
My three oldest tanks were originally setup with plain sealed aquarium
gravel or sandblasing grit over ugf plates. It took a while for mulm to
build up, but once it did those tanks managed to support good plant
growth. My newer tanks and emergent sword setups were built with a
mixture of aquarium gravel and peat with either a small amount of soil
or chelated iron mixed in. The difference between these setups is not
so much in their ability to grow plants, but in the amount of time it
takes to get good growth and the amount of iron and other amendments
that the plants need added on a continual basis.
Plants thrived from the start in the substrates with peat/soil and
peat/iron, but with plain gravel it took months for the mulm to build up
enough to do a good job of supporting plants. The gravel/mulm substrate
continues to change for several years after it's set up. Also I found
that fine sand works very poorly in that sort of setup, because the mulm
has little tendency to sift into it.
I have to continually add iron fertilizer to the plain gravel tanks. I
do that with iron gluconate tablets in the substrate at the base of the
plants, so I have a pretty good idea of which plants need the most iron
and how much they need. The plants with gravel plus peat/iron or
peat/soil require far less iron fertilizer. In fact my emergent swords
with the peat/iron substrate haven't needed any additional iron
fertilizer since the day I set the first one up about a year and half
ago, but the plants grow and reproduce at a remarkable rate.
The differences are really noticable when you grow root feeders like
sword plants. And the differences aren't limited to iron fertilizer. I
find that sword plants in the gravel+mulm substrates need more calcium
additions and more nitrogen (jobes spikes) then do larger and
faster-growing sword plants in the gravel+peat/soil or gravel+peat/iron
The same comparison is true for at least some crypts, but with crypts
the differences are smaller. Even some stem plants grow with less work
in the gravel + peat/soil substrates.
Gravel + peat/soil or peat/iron aren't real special substrates, they're
just what I use. Other people can make the same claims and comparisons
for other sorts of substrates, including the commercial preparations.
You can make a plain gravel substrate work, but it takes more time and
effort than other options. A gravel+laterite substrate is no different
from plain gravel unless you grow root-feeding plants *and* set up
conditions where the laterite can work to your plants' advantage.
> For a beginner I would tell them to save
> their 20-40 dollars and put it towards CO2. But, of
> course, I am willing to be educated.
For a raw beginner that may be pretty good advice. For someone who's
been here before and wants to improve their setup, or for someone who
wants to make I fast start, I would say that they need both an improved
substrate *and* CO2.