I found the following information regarding this species (the 2nd and 3rd paragraphs are of particular note here)...
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The Singapore Angelfish, also known as the Vermiculated Angelfish, has been likened to a butterflyfish in body structure. Blue lips and a yellow nose abruptly change to a black vertical band over the eyes, resembling a mask. The mask is bordered with another thin vertical band of yellow, followed by a wider vertical band of white with the body being primarily black. Dorsal and anal fins are outlined in brilliant sapphire-blue and the caudal fin is usually yellow but may be gray.
The Singapore Angelfish can be challenging to keep. Some acclimate well, while others hide constantly and do not eat. Providing a quietly-located aquarium with non-aggressive tank mates and plenty of hiding places may help.
A minimum of a 55 gallon tank or larger provided with live rock for grazing will also help provide an optimal environment. The Singapore Angelfish is prone to nip at stony and soft corals (sessile invertebrates) and clam mantles. It will also graze on microalgae, filamentous algae, and diatoms. The diet should also consist of mysid or finely shaved frozen shrimp, and other meaty items.
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Hope this is helpful.