Can someone explain once and for all the "altum" angel. There's only one right?
Depends on who you ask this question to!
IMHO the ornamental fish trade is happy to "muddy the water" by describing several attractive Scalare variants as "Altum", "Peruvian Altum", "Altum peruensis" etc.
The other P. Altum (the real one!) was originally collected (and described) from the Orinoco drainage. This is a larger fish than the Scalares having a tall body, accentuated by tall fins (especially noticeable on juveniles), wider bars (the colour of which it can vary from sepia through browns to jet black, according to mood) ochreish scribble markings and blue suffusion on the dorsal contour, a solid "comma" mood spot on the operculum (again displayed according to mood), a larger eye and mouth than the Scalare, and a horrendous mortality when newly imported.
To pile on the confusion, several people have asserted that the "true" Altum also inhabits some of the upper parts of the Rio Negro drainage. Heiko Bleher is insistant that the Rio Negro fish are a lovely Scalare similar to the Orinoco Altum (having somewhat shorter fins) but breedable in captivity, hence, he asserts the source of the line of tank bred fish from Horste Linke.
In captivity at least, the Orinoco type Altum shows a lesser fin to body ratio when adult, the body tends to bulk up, but the fins do not appear to increase in proportion, so the adults do not exhibit the extremely elegant proportions of the juveniles.
to add a bit more confusion, all the characteristics of the Orinoco fish with the possible exception of the large eye, mouth and solid mood spot, appear to occur in individual Scalare variants. Still confused? you should be, working out the lineage and source of these lovely fish is very much a work in progress.