Re: biomedia in planted tanks

["S. Hieber" <shieber at yahoo_com>]

Greger Lindstrand asked about sand filters:

> Would this work?
> 
> I've seen in a pool shop, that the cleaning aparatus of a swimming
> pool is just a big cannister filled with sand, 2-3 mm grain size and
> a pump to run it. . .
 
> Would such a setup work for a planted aquaria?
> I could hide the thingy (it's big) in the basement, so apperance
> isn't an issue, but would it work?

Sand filters are much more popular in England than the USA -- not
counting UGFs & RUGFs which are internal sand filters.

The pool type is big and simple, usually just one stage.  Aquarium sand
filters are more often multiple stages, which finer sand particles in
each stage.

You can make one by putting sand in tub (or 2 or 3 grades of sand in 1
or more tubs, and route the water through it.  This can be done sump
style with screens between the sand-grades or with siphon hoses between
the tubs.  You could start with gravel/sand thats about 3 mm or the
size of flourite, and work down to 1mm filter sand.

You can even do this "trickle" style so that the sand is never
submerged, trays of finer sand are placed below coarse grades.  This
should reduce the amount of sand needed to be effective in a given
situation.

You can achieve the same increase in effectiveness with much less sand
by going the fluidized bed route --- super fine sand (lots of surface
area) in a current strong enough to lift the sand and keep it from
settling.  As long as the sand is lifted, its surface get exposed to
new water.

For sand filtration, you need some good coarse mechanical filtration up
front of the sand or it will clog quickly, become packed and
ineffective.

I suppose you could use a pool filter as a central system for lots of
tanks running off plenum lines.  But they are designed to handle a lot
more water than most aquarists have tanked at any one time.  Of course,
otoh, the aquarists' tank inhabitants put more, er, bio-degradable
material in their tanks than the pool owners' tank users.

An alternative to sand, for pools and aquaria, is diatom filtration, in
which case you flush and load new diatoms instead of backwashing
(rinsing) the sand.

Scott H.

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