What types of fish are best kept with Angelfish

Jesus fish. (kidding)

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You can't go wrong with platies. They are loaded with color, and what's good about those is the males & females are equally colorful, so you can have really nice, bright splashes of color all over the tank.

You can have 1 rainbow shark. They don't really like fish of their own kind too much so it's not recommended that you add more than that, but your tank is definitely suitable for one. You've got lots of water volume and swimming room for when they feel like darting around.

Swordtails are similar to platies, and tend to be more aggressive, so you may want to pick one species (platies vs. swords) over the other.

Serpae tetras are a good choice becuase they're kind of testy like the angel, and the rainbow shark, so a school of these would definitely fit right in.

Rummynose tetras are white/red/black so they'd be a good color contrast with the platies and the angel, and they school tightly, so if you like that kind of display, they would be another nice choice.

A really pretty fish that you might like is the Dwarf Australian Rainbow. These are a lovely blue shimmery color, and the males have orange fins and the females have yellow fins. They don't photograph well at all, so pictures don't do them justice, but they would be GORGEOUS with that angel! They're a really "classic" looking fish that will never go out of style. They're not cheap, though, but that's actually a good thing because it means you'll have something different that a lot of other people won't.