"andy" wrote in message
...
Using a few well placed rocks and pebbles would allow the available
sand to
be spread over a smaller area, ie around those items of decor. This
would
allow for greater depth of sand which is essential so as not to expose
the
roots of any plants in your tank. Only use rocks bought in aquarium
shops,
don't be tempted to use ones found in gardens or on beaches etc. They
may
well be contaminated with unseen polutants!

Your well intentioned advice, to use LFS rocks, will keep hobbyists out
of trouble, but it's certainly not economical on anything but the
smallest aquariums. There are many ways to ensure that rocks you pick up
are safe. I cut the following out of a web site (my own, under
construction):

Not all rocks are aquarium safe (copper is extremely toxic, starting with
parasites, then invertebrates like snails and then to fish in higher
concentrations), or aquarium suitable (due to their size, shape or effect
on the water). Some rocks are completely inert (will not react with
water like slate or granite), while others are very reactive (Utah Ice
melts in aquarium water). The greater the porosity of the rock, the more
potential for hazard (or benefit) it has. This includes pathogens (from
stones from natural freshwater environments), to anything which might
leech out (typically natural calcium, but may include toxins).

The rocks found in your local pet shop will generally be completely safe,
but will include both inert and non-inert types. The retail cost is
quite high, mostly reflecting the cost of transport, and not the actual
materials. If you are stocking a small aquarium, or are just looking for
a few unique pieces not found in your area, or natural stones are not
available where you live, (or they are under a foot of snow), then
consider pet shop rocks. Although they have the highest prices, they may
also have some of the more interesting types to tempt you (ie: petrified
wood, zebra rock, rainbow slate etc). For any significant amount of
rocks, visit your local quarry and home renovation stores to compare
price & availability. Rocks collected from natural environments can also
be used. Contact your local aquarium society to see when they are
planning their next trip, as they usually know the best places to go.

A simple test it to drip a strong acid on a rock and observe the
reaction. If it fizzes, then it will leech calcium into your water,
making it more alkaline and harder. Vinegar is a bit too weak an acid.
The pH-down product is a satisfactory tester. I think the acid reacts
with the carbonates, which generally indicates a high degree of calcium.
The test is not completely accurate. Minerals low in carbonates may
still leech calcium (ie: Utah Ice), and some minerals may cause the pH to
drop in the right conditions.

Avoid green in rocks as this is the color of copper in a normal oxidized
state, and copper is toxic. One test method is to put a representative
sample of the rocks collected in a pail of water with some fish (ie:
white cloud minnows). If after a week or so, the minnows are fine, they
you have some degree of confidence that whatever the rocks might have was
not toxic in the high concentration which would have built up in the pail
of water.

NetMax