The 5.0 is as likely to make the Nannostomus spawn as it is the Dicrossus. They occur together in nature, and enjoy the same type of habitats. The dropping to 5.0 from 5.5 is what occurs during the dry season. However, Pencils are not top dwellers so much, they basically stay midwater and near the substrate, much like the Dicrossus. Something like one of the Dwarf Hatchets, Genus Carnegiella (Marbles and Black Wings) would definitely stay at the surface, and also prefer the very low pH ranges. C. marthae and C. myersi are difficult to find, but Marbles are usually pretty common.
My experience has been that dithers don't help much. Dicrossus are just natural hiders, they slink around even when they think they are safe. They only seem to display when courting, as males are not territorial - females are. Their breeding pattern reflects this shy nature, in that the eggs are usually somewhat hidden, and the female tends to stand away from her eggs so as not to draw attention to them. Should anything threaten them, however, she is very quick to come in and defend them.
