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smelly soil substrates
I'd like to add a little to Karen's observations and precautions on
selecting soils for the aquarium. On the weekend I was looking for
some top soil to incorporate into my 75 gallon tank which I'm redoing.
At a local nursery/garden center I found a pile of nice black soil for
sale; U shovel, 3.50 / bag about 75 lbs (humpfffhh) and it was called
garden soil. Since it tends to rain a lot, the stuff was pretty water
logged. Took it home and opened the bag, -yuck-! a powerful H2S
stench! I took it back for a refund. Yesterday I cruised another place
and found the same smelly stuff also labelled "garden soil" but
another pile nearby was labelled top-soil and it did not have the
nasty smell. I also found out after talking with one of the nursery
specialists that this soil works fine in gardens and is dug up by a
local company from a bog (first clue). What makes this soil go "sour"
(get H2S)? it is a heavy clay soil, it has a lot of organic material
in it and it is submerged. It also probably doesn't have the benefit
of aquatic or semi-aquatic plant roots growing through it to oxygenate
the soil. I'll also bet that it has a fair amount of sulfates and not
enough iron in it. My feeling is that our local BC soils are very low
in iron content AND they are also very heavy clays. Iron compounds
will react with H2S and form FeS.
Moral: use your nose when getting soil. Avoid a sour smelling soil. It
already has high H2S content and that's definitely going to inhibit
the growth of your aquatic plants.
A strong smell could also be ammonia and this is not really a problem
(although any soil with enough manure to smell of ammonia is probably
too rich to be used without mixing with sand, gravel or vermiculite)
The ammonia smell is easy to learn; it's the smell of manure or just
take a whiff from the ammonia cleaner bottle.
H2S smell is the smell of natural gas. It is a petro chemical smell.
Your nose can detect H2S in concentrations in parts per billion.
When you take up an aquarium pot or soil, I wouldn't be overly
concerned with a mild ammonia smell but an H2S smell means you have
too much organic material, probably too much sulfate (possibly from
fertilizers made from sulfates) and not enough vigorous plant growth
to keep the redox potential of the substrate at a safe level. (recall
the plants provide oxygen in the substrate through their roots)
As for the use of chemical fertilizers like osmocote: short term
evaluations probably won't show problems like sulfer accumulation. The
less sulfer in the fertilizer the better IMHO if you intend to put it
in the substrate.
Steve in Vancouver where the sun has finally put in an appearance! :-)