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Substrates for Planted Tanks
There are many different options when it comes to substrates for a planted
tank. Flourite, Profile, kitty litter, vermiculite, sand, gravel,
topsoil from your garden, peat, laterite, the list goes on and on.
All of these substrates can be effective, and can produce nice planted tanks.
There are many proponents of each, and advantages and disadvantages. I'll
run down each one.
First, a couple definitions:
- Inert:
I use the term to specify that the substrate won't alter the water
chemistry. That's a good thing in a substrate.
- CEC:
Cation Exchange Capacity : the ability to adsorb positively charged
nutrient ions. This means the substrate will hold nutrients and make
them available to the plant roots. A high CEC is a good thing. It
doesn't indicate the amount of nutrients the substrate contains.
- Flourite:
A great substrate. High CEC, inert, very nice looking.
Nutrient rich, but the nutrients are only available to plant roots. They
will not leak into the water column. Contains iron and other trace
elements. Doesn't get soft in water. $15-$20 per 15LB bag.
- Profile:
A good filler. Inert. Doesn't get soft in water. High CEC,
tan/light brown in color. Contains no nutrients. Lighter in weight
than Flourite or regular gravel. I had some problems in an experimental
tank that used 100% profile, even with 3" of profile, the substrate was
unable to hold some plants down. Sold as "Schultz Aquatic Plant Soil",
or "Schultz Clay Soil Conditioner". $10 for a 40LB bag at Home Depot.
- Kitty Litter:
Varies greatly by brand. Some are inert, others will
drastically alter your water chemistry. Many (all I've tested) will
eventually get soft and mushy in water.
- Vermiculite:
Inert. This is a soil additive that has an extremely high
CEC, and contains some trace elements. It's very lightweight and needs
to be covered with a layer of heavier material to prevent it from
floating.
Very messy to work with. I had some in a test (plant only) tank and even
after two months, a bunch would float up whenever I added/removed a plant
from the substrate.
- Sand:
Inert. No purpose other than to hold plants (and lower layers of
other substrate) down. Low/no CEC.
- Gravel:
Any gravel made for aquariums should be inert. If you are
buying bulk, you can drop some into a cup of vinegar. If it fizzes, it
isn't inert, and will harden your water. Even if you have soft water,
that isn't a good thing, as you won't be able to control how much it
hardens it. Most gravels have a low CEC, and contain no nutrients.
- Topsoil:
Lots of organic material. This creates a very rich substrate,
too rich in my opinion and experience. Leads to lots of algae growth,
from the endless supply of organic nutrients into the water. Also,
leads to areas in the substrate that will rot, killing off the plants in
that area. I avoid using any organic material for my substrate.
- Peat:
Again, organic. Will alter water chemistry, softening water and
lowering pH. If used (if you want softer water), it should be under a
layer of some non-organic substrate (sand/gravel/etc)
- Laterite:
Purely a substrate additive. It's a rich red clay. Inorganic,
and inert. It's very rich in iron and some other trace elements. Must
be mixed with a regular substrate, and buried under a layer of some
regular substrate. Otherwise, the iron and nutrients will enter the
water column, clouding the tank, and resulting in extremely high iron
levels, which will lead to algae problems.
So, lots of choices. Want a simple recommendation? I suggest 100% flourite.
The only downside to flourite is the cost. For larger tanks, it can get
expensive. If you want to save a buck or two, mix it with Profile (no more
than 50% profile, preferrably no more than 25% profile).
Substrate is probably the hardest thing to change
at a later date. You are stuck with it. Using rich organic
substrates will eventually produce problems with water quality
and excess nutrients. Using cheaper alternatives (like the
kitty litter) has a chance of working, but if not, you've got
a huge mess on your hands. And even the best brands of kitty
litter won't contain the nutrients that Flourite does.
As for additives like laterite: Some people like to use
laterite mixed into an entire layer of substrate. This is
making the entire substrate very Iron rich, but it's not needed
everywhere. A better alternative is to get a small bag (several
ounces) of laterite, mix some in a bowl with water, and make
small (1/2" in diameter) laterite balls that can be pushed down
into the substrate at the roots of the heavy root-feeding plants
(like amazon swords!).
As I said at the start, there any many paths to success. Any of the
substrates mentioned, and many others not mentioned, can and have been
used successfully. But for me, I want a substrate that is low
maintenance, and stable. I don't want something that over time is
going to mess with my water, or constantly change the water chemistry.
Layered substrates get disturbed regularly by planting and by fish, and
release nutrients into the water. Organic substrates release substances
into the water that alter the pH or other chemistry.
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Your feedback on this article would be greatly appreciated. All feedback is
anonymous, so please, be honest. Your input can help me create better content.
If you have any questions about this article, or if you feel that something is
incorrect or missing, please let me know via email at cgadd@cfxc.com
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