I'd say: go with what adapts best with the tapwater!
your tank will most likely be a sort of "community cichlid living room tank" and that means you want:
-easy to keep fish, sturdy and tough
-active fish, not hiding all day
-fish that react positively to people (kids?) coming close to the tank
-colorful! goodlooking. no uglies allowed
fish like that eat a lot, swim all day and poop all night
hence, you need to be able to change fair amounts of water without getting all kinds of issues.
you don't want to fumble about with ktion/anion exchangers, rho-water, rainwater etcetera.
what is your tapwater like?
if it's fairly soft; South American cichlids can be kept; this includes Adinoacara (Green Terror), Oscars and a lot of other colorful beauties like the Xingu Pike, large characins (Metynnis aka Silver Dollar), Heros, Geophagus etc
South American catfish include a zillion kind of pleco's (better known as "L numbers"), many of wich have striking colors and patterns, for example the Panaque or the Gold Nugget are true beauties. ditto the gracile Sturisoma, the skitterish Pimelodus or the tame Hoplosternum.
Clown Loaches originate from water that is virtually the same as Amazonian water and do fine in a large South american tank.
if it's hard Central Americans are the way to go.
many of them are so colorful it's almost trippy (Vieja synspilum comes to mind), others have great personality like the Parachromis and of course the Jack Dempsey wich is also very colorful and very easy to keep
there aren't many catfishes from Central America. the sturdier SA catfishes will do fine with them; like Platydoras, Hypostomus, Ancistrus etc.
also a great combi with CA cichlids are the larger African Synodontis like Synodontis eupterus, S angelicus (stunning fish), S schoutedeni, S longirostris etc
I know that many tapwatercompanies keep their tapwater in the midrange with hardiness and boost the pH up to 8.
this they do because in water like that, copper doesn't dissolve.
soft acidic water dissolves minute amounts of copper (pipes are made of it) and that amount of copper is no good in the human body, it's a toxin.
hence the pH 8 buffering. keeps you healthy.
if your tapwater is REALLY hard and alkaline then Tanganyika is the way to go.
frontosa's are the "Oscars of Africa" with similar behaviour and a lot of personality too.
Riftlake Synodontis are truly gorgeous and as catfish go extremely visible. they are also for sale in a lot of places.
they range from the tiny captive bred Synodontis lucipinnis and S petricola tothe majestic and horribly expensive Synodontis granulosa wich is the Emperor among African catfish.
there IS another possibility.......
if Reeftanks are your thing, but you don't want to go thast way because of the money tag; if large active and above all tame handfeedable true beauties that co-exist with catfishes ansd are kid-resistant; I can recommend Madagascar........
specifically Paretyroplus maculatus or P menarambo.
these are shoaling fish! yes, a true shoaling cichlid. the bigger the number, the more fun.
in a 300G tank you can keepa fair sized group
they reach a fair size, they're incredibly tame, they are very easy to keep if you forego breeding and they can be kept with almost any characin, barb, loach or catfish.
they always remind me of Surgeonfish. the blue Dory in Finding Nemo.
except that Paretroplus is green with red, grey and gold. the shape is almost the same and the swimming as well.
all Paretroplus are captive bred nowadays and they adapt to any water as long as it's clean.
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