Phenols represent a broad class of aromatic
organic compounds that persist in aquarium
water. Humic substances like tannins are
just one group of polyphenols. Phenolic compounds
arise as metabolic byproducts in plant cells.
Plants quickly void them into enclosed vacuoles
for safe storage, because they would interfere
with plant metabolism.
Polyphenols link molecular phenol rings into
chains to form complex water-soluble organic
compounds. Various polyphenols are anti-oxidants;
they provide the colors of ripe plums and
berries; they impart intense colors to geraniums
and delphiniums. The shorter chain polyphenols
are soluble; longer chains are insoluble
and go to make humus.
Phenols can be strong systemic
poisons for
protists and animals too.
Stored in the tissues
of plants, phenolic compounds
deter plant
browsers, but they are
released when plant
material decomposes. When
senescent plant
cells spill their contents
into the water,
polyphenols are among the
first chemicals
to bleed away. Once they
have dispersed,
within 24 hours, the pioneer
bacteria and
fungi start colonizing
the surfaces. You've
often noticed that snails
will attack softened
leaves, but leave firm
green ones un-nibbled.
Phenols released by plants have a repressive,
"allelopathic" effect on some algae. Phenol in concentrated
form is even used as an industrial antiseptic,
cautiously, for phenol and its derivatives
are only marginally more toxic to microbes
than to multicellular organisms. Though pure
phenol produced in a lab is colorless, phenol
that is degraded by sunlight, or the aquarium's
naturally-occuring polyphenolic compounds,
which aren't perfectly pure, normally lend
the water a yellowish or rusty cast. Phenol
itself is particularly sensitive to oxidation.
Good aeration-- or hydrogen peroxide-- breaks
down phenols. There's a good posting on phenols
in particular and allelopathy in general
at the aquatic-plants
digest.
Other polyphenols form complexes with animal
proteins, useful in tanning hides. Tannins
are particularly concentrated in the bark
of many trees. Oak bark, for instance, is
still used for tanning hides. The polyphenol
quercetin, derived from bark of the red oak,
produced a strong yellow dye that was shipped
to England in colonial days. Similar polyphenols
discolor the aquarium water. That is one
reason for removing the bark from wood meant
for an aquarium, though other aquarists might
actively want some of those tannins and other
golden polyphenols. A desirable aspect of
tannins and humic acids is their effect as
chelators that keep nutrients available to plants
and mitigate the toxicity of metals
Green tea. If you make peat tea for its softening and
other benefits, it's hard to get a full run-down
of the chemistry you're introducing to the
water. But if you add a cup of green tea
instead, the chemistry has been done for
you. A document at The Way of Tea website,
"The
Chemistry of the tea leaf" gives detailed
analysis of what a "tincture
of Camellia sinensis" has to offer in the aquarium, viz:
inorganic salts, headed by potassium (1.76%
of dry weight), that include traces of the
plant nutrients phosphorus, magnesium, iron,
manganese, sulfur and others;
nitrogen in soluble protein and amino acids
as well as in caffeine (caffeine itself isn't
very soluble-- the boiling water releases
it.; so if you think it might keep the fish
up all night., drink the green tea and just
put the used teabag in the filter);
more nitrogen in tiny amounts of sugars and
starch and larger amounts of pectin; some
chlorophyll and other pigments, enzymes and
vitamins B2 and C (in unfermented green tea);
the most important chemical components of
tea leaves, a series of flavonoid polyphenols
called catechins, based on gallic acid, among
the currently fashionable "anti-oxidants"
that scavenge free radicals.
Now, where was I reading about the aquarist,
faced with an intractable pair of Apistogramma, who had tried everything to induce spawning?
He was intently inspecting them, when he
spilled his mug of black coffee into the
aquarium. They spawned the next morning!
