Some of my slower growing plants, with large leaves, seem to be afflicted by
lots of little pin prick sized black spots.

This seems to be a type of algae but I cannot seem to find much information
about this particular form. It is impossible to scrape off, the only thing I
can do is remove the afflicted leaves.

My tank is well planted and all seem to be doing quite well, and Nitrate is
holding at 25ppm. Other tank specs: Co2 Injection at around 1 bubble a
second, PH at around 6.8. Lighting from 2 x 30" Arcadia Freshwater tubes.

Any ideas?

Thanks

JFM