So what does it say under Tank compatibility
Pterophyllum altum
Best kept in a single species or specialized "Guyana shield or Orinoco Blackwater habitat" aquarium containing species of the same habitat. Other species within this habitat: Satanoperca daemon, Guianacara sp., Uaru fernandezyepezi, Mesonauta insignis, Dicrossus filamentosus, Apistogramma iniridae, L128, L200, Paracheirodon axelrodi, Hyphessobrycon bentosi rosaceus, Hemigrammus rhodostomus, among others. Note that smaller fish such as Paracheirodon axelrodi will as a rule be eaten.
Pterophyllum scalare
Compatible with some South American Cichlids such as the German Blue Ram or any of the Apistogramma species. Do not keep with small tetras or other small fish 1.5" (3.8cm) and under, they may well become lunch, or overly aggressive fish. Avoid known fin nippers such as Tiger Barbs or Serpae Tetras. Other territorial mid-top dwellers such as Betta splendens and Gouramis are not advisable either as they may become too curious towards the Angels.
As i said there is a chance that the Angels will once Adult size prey on Tetras, He may get away with it like the way you said you have but its all a risk!