One CUBIC inch per gallon. An angel is round, so I guess you could do six, though once they pair you might have problems
:iagree:. i hate that rule with a passion:swear: it literally makes no sense.The inch per gallon guideline is absolute garbage. Your 55g can fit about 6 angelfish just fine although of course, you need a backup tank since angelfish will readily pair up as they mature and can bring problems to the community in the process.