On Wed, 01 Sep 2004 09:25:56 +0100, Nikki Casali
wrote:

I have 4 clown loaches and they are completely covered in a very fine
powder. I have been treating them with white spot treatmenr for 2 weeks,
but the "white spots" remain untouched.
....
In all the 15 years I have been keeping fish I have never seen such fine
microscopic spots.

Sounds like Chilodonella.

25 ppm formalin repeated three times with three days between each
treatment, and a large water change 24 hours after each treatment,
took care of what was likely Chilodonella here. Recovery was almost
instant, within a few hours of the first treatment fishes were free of
any symptoms.