82
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Equipment
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fish which do not tolerate plants in their environment can
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theless enjoy the benefits of water from a planted aquarium. Many
other
advantages result from this system, and of course, with
g00d usage, one ancillary environment may well support more
than one primary environment.
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The principles of biological filtration have already been explained
at length, but some consideration of the construction and installation
of sub—gravel filters (Figure 30) is worth while. At the present time
these are still being developed, and this is one field in which the
practical aquarist can often improve on commercial products, and
indeed is even obliged to in many cases because filter plates just
cannot be bought ready-made to fit every size and shape of aquarium
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(a)
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Fig. 30. The sub—gràvel filter. An_air-lift .draws water'fr0m beneath the
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Which is replaced by water from above. A filter bed (of gravel) is therebypro'vided
with & steady circulation of oxygenated water, which facilitates the
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removal of toxic substanèes by aerobic bacteria. (a) An exloded. diagram, show-‘
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joined, and operated by one air—lift:
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jl, filter plate; 2, mixing chamber; 3, blanking plug; 4,_lift tube; 5_, joihing…clip;,
6, diffuser stone (Courtesy North We'St Plastics)l (b) A sub—grave] filter in position
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(gtavel cut away for illustration). (CourteSy Algarde Plastics)"'
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