I commend you on your descision to use oak leaves. These are, in my opinion, one of the best ingredients for substrates. I usually top off bare gravel or gravel covered in long fiber sphagnum moss with oak leaves. As far as cleaning them, that is not a factor and in fact, by using straight from their source, you would be introducing springtails and other microfauna to your vivarium which would be highly beneficial. WI break the leaves down into smaller pieces and lay these down over the substrate then top that off with a few medium sized leaves here and there. I also leave a few bare patches here and there to grow live moss...especially under areas that recieve the most light. The leaves will eventually break down and this will, in turn, provide the good nutrients for you plants. The tannic acids in the leaves also aid in keeping the water at a nice acidic level. In my experience, the usage of leaves in the viv often brings out even the shyest of species and makes them feel more secure. The benefits are countless and your choice is a great one. I hope this helps to answer your questions.
-Bill J
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Updated list as of: 11/7/03
2.2.3 D. azureus
1.2 D. ventrimaculatus 'yellow' (22 tads in the water)
3.3 D. tinctorius 'cobalt'
0.0.3 D. tinctorius 'patricia'
0.0.1 D. tinctorius 'giant orange'
0.0.1 D. tinctorius 'citronella'
0.0.2 D auratus 'zwartgroene(Panamanian black and green)'
0.0.5 D. auratus 'green/black'
0.0.3 D. imitator 'Alex Sens line' (very soon)
0.0.2 D. reticulatus (soon)