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Would I be able to put a Synodontis Petricta & a Synodontis Angelicus in with 3 or 4 4" Hypancistrus in a 30 gal. tank 36" x 12" ?

what are your water parameters?

the petricola likes hard alkaline tanganikan water, while the hypancistrus and the angelicus prefer soft acid water.

you may be able to compromise straight down the middle. i'm not sure how adaptable the petricola are.

they may be a bit of aggression. make sure there are lots of hiding places.

there will also not be enough room when the fish reach adult size. that will take many years though, provided you buy juveniles.

a bigger tank will be needed long term.

no.

first: the petricola is a sorry, lonely fish that is kept in the wrong water with the wrong company. it needs hard, alcali water to thrive, although it can survive on neutral mediumhard as well.
it should be kept in a group; and your tank IS big enough to keep 5 or so.

next the angelicus is a BIG fish or it will be; and quite territorial, esp in a small tank. S angelicus easily reaches 8" or so, and needs a 75G or bigger to be happy.