[pineapple]

I can't explain it, but have thought of it as a process of innoculation. The system is infected then developes an immunity. Some things are hard to explain, for example in that post in which you (Niko) noted that the glass exposed to air during a water change does not develop algae again, or that Anubias exposed to air in the same process do not get algae.

The mysteries of life remain hidden in our crystal boxes..

Andrew Cribb