On 02/01/2012 15:26, Graham. wrote:

I discourage any living organisms in my fish tank except the fish!
Plastic plants, no risk of introducing those little snails that you
can't get rid of, and very little algae.

Assuming this is a freshwater tank....
You need to encourage nitrifying bacteria at the very least - normally
in the pump filter. Otherwise you'll get a build up of toxic ammonia.
The bacteria convert excreted nitrogen compounds to nitrite, then
nitrate, which would (normally) then be used by live plants.

Without live plants the excess nitrate encourages algae. Assassin snails
are very good at controlling plant snails.

Finally (IMHO) plastic plant just looks awful.

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