5.1 Natural or synthetic?
5.1.1 Natural
Natural seawater has much to recommend it. It is 'alive', which can
have positive effects for filter feeding organisms, has the right
balance of chemical substances in it, and is free.
BUT, assuming you don't live 20 metres from the next coral reef, things
may be different.
You may have noticed (live or on film) that the seas where our
creatures come from are bluish in colour. Although reefs seem to be
teeming with life, they are local oases in what is really a watery
desert. The waters of the North Sea and North Atlantic are green. The
colour is due to the much higher levels of nutrients and plancton in
these waters. Although nutrients may not present a problem, this isn't
true if you collect anywhere near sewage outfalls, rivers, or beaches
where cows might be grazing.This presents a possible problem for the
aquarist. So collect well out to sea or at least from an isolated rocky
coast. Transport the water any distance, or heat it, the dead
planctonic life may be a considerable source of pollution. There may
also be the small chance of disease, but this is negligible in
comparison to adding a new animal to your collection.
5.1.2 Synthetic
Synthetic seawater is made by taking a ready- mixed bag of aquarium
salt crystals and dissolving it in water. Using brand named salt mixes
will ensure a good quality. One product is made by evaporating clean
seawater and selling the resulting crystals. Otherwise, these mixes are
made up of single component salts of high quality (the manufacturers
usually talk of 'analytical' grade, which means the individual
substances are pretty well as pure as the chemical industry can get
them).
The word 'salt' defines a particular type of chemical substance of
which 'common salt' is just one.
Most of these salt mixes, when made up with reverse osmosis water,
create a seawater which is not identical with natural seawater.
5.2 Filtration:
or how we get the crud out! Mainly food remains and fish faeces. The
nideal system, which may be comprised of more than one component does
this: NH3/NH4+
> NO2+ > NO3+ then NO3+
> N2
There is no bacterial way to remove phosphate- this needs either algae
or a chemical means.
Adding calcium hydroxide to raise calcium levels may well precipitate
solid calcium phosphate, but there is always a small chance this can
reverse under unfavourable circumstances. Proprietary removers are
better (e.g. Rowaphos, or others)
Berlin
system-
use of live rock and skimmer (usually in filter sump). Live rock has
aerobic
and anoxic reductive areas to convert any waste nitrate to nitrogen.
Jaubert system- use of a
'plenum'-
a depth of 10cm or so broken coral or coral sand either directly in the
aquarium
or in the sump. This lies on a perforated plate fixed 1cm or so above
the
tank base. Small creatures encouraged to burrow in the top layer.
Milieu changes
with depth from aerobic to reductive. Layer depth a problem in a small
tank
Algae filter- will remove
nitrate and phosphate when you harvest the algae
Sulphur filter- must be
combined with calcium carbonate to remove sulphuric acid. Can disturb
calcium/ alkalinity balance.
Miracle Mud filter- seems to
work very well in a sump, no personal experience
Filters that don't do the business
in marine reef setups: trickle filters,
undergravel filters.